USOpen.org looks back on two weeks of sizzling tennis at the most demanding of Grand Slams: the US Open. Here are 18 takeaways from the fortnight.

1) The new Louie is sublime. Tennis junkies mourned the loss of the old Louis Armstrong Stadium, which had played host to many a historic battle through the years: 39-year-old Jimmy Connors’ epic fourth-round 3-6, 7-6, 1-6, 6-3, 7-6 triumph over Aaron Krickstein in ’91; the Super Saturday extravaganza of ’84 (viewed by many as the single greatest day in tennis history), the 11 a.m.-11 p.m. semifinal marathon that featured seven future Hall of Famers, including John McEnroe, Jimmy Connors, Martina Navratilova and Chris Evert. But even the old-school purists were quick to praise new, roofed, 14,000-seat Louie, which maintains the intimacy and sightlines of its former namesake. Croat Marin Cilic (2014) and rising Aussie Alex de Minaur would provide the state-of-the-art facility with its first late-night marathon, with the 2015 titlist closing out a thrilling five-setter, 4-6, 3-6, 6-3, 6-4, 7-5, at 2:22 a.m.

August 30, 2018 - Novak Djokovic in action against Tennys Sandgren during the 2018 US Open. (USTA/Pete Staples)
Photo by:  (USTA/Pete Staples)

2) It’s gets hot in New York in August + September. They call them the dog days of summer, after all, but the heat and humidity rose to new levels in 2018, leading to the implementation of new heat rules in order to bring relief to the players. Said Britain’s Johanna Konta, "It was bloody hot." Novak Djokovic went a step further, declaring, "This has been definitely the toughest US Open in the last 10 years."

September 3, 2018 - Roger Federer exits Arthur Ashe Stadium after losing against John Millman during the 2018 US Open. (USTA/Brad Penner)
Photo by:  (USTA/Brad Penner)

3) Roger Federer is human. Some 20 years and a like number of Grand Slam titles into his history making career, Sir Roger has us all rethinking the lifespan of a professional athlete. At 37, the Swiss is still very much at the top of his sport, having earlier this year won his sixth Australian Open title and reclaimed the No. 1 ranking. But the No. 2 seed struggled in his US Open fourth-round matchup with Aussie John Millman, who would score the upset of his life. Said the five-time champion afterward, "It was just one of those nights where I guess I felt I couldn't get air. I don't know, for some reason I just struggled in the conditions tonight. It's one of the first times it's happened to me."

September 05, 2018 - A superfan watches a Junior match between Clara Tauson and Dasha Lopatetskaya at the 2018 US Open. (USTA/Mike Lawrence)
Photo by:  (USTA/Mike Lawrence)

4) You never know what's going to happen. Fans dunking chicken fingers in Coca-Cola. Chair-ump controversies. Floss dance-offs. Moldovan super-supporters. On-the-edge-of-your-seat, late-night/early-morning marathons that stretch until 2:22 a.m. Expect the unexpected at the US Open -- part Grand Slam, part tennis carnival.

play video Press Conference: Simona Halep, Round 1

5) Simona Halep is still a work in progress. (For that matter, so is Sascha Zverev.) Yes, Simona Halep finally got over the hump in Paris, cementing her No. 1 ranking with her first Grand Slam crown at Roland Garros. But the Romanian is still finding her way when it comes to playing consistent ball all year round at the majors. She took a step back in New York, falling in the first round to No. 44 Kaia Kanepi, 6-2, 6-4, becoming the first No. 1-seeded woman in the Open era to lose her opening match at the U.S. Open. Similarly, Alexander Zverev is still finding his way at the sport’s Big Four events. The fourth-ranked German has certainly made his mark at Masters 1000 tournaments and owns wins over the likes of Roger Federer, Novak Djokovic and Stan Wawrinka, but he has only once (2018 Roland Garros) advanced beyond the Round of 16 at the majors. The 21-year-old lost to fellow German Philipp Kohlschreiber in the third round at the US Open, 6-7, 6-4, 6-1, 6-3.

August 27, 2018 - David Ferrer during a post-match interview at the 2018 US Open. (USTA/Garrett Ellwood)
Photo by:  (USTA/Garrett Ellwood)

6) Goodbyes are never easy. Pete Sampras famously (and tearfully) announced his retirement at the US Open in 2003. Archrival Andre Agassi bid farewell three years later, crediting the Ashe Stadium denizens for pulling for him even in his darkest moments. "You have given me your shoulders to stand on, to reach for my dreams — dreams I could never have reached without you," said the Hall of Fame-bound Las Vegan. Andy Roddick played his final match in Flushing Meadows in 2012, his vanquisher, Juan Martin del Potro, stepping back to allow the crowd to show their appreciation for one of the tour’s steadiest performers. The US Open has been the site of some memorable farewells. This year, we said goodbye to two-time semifinalist David Ferrer, 2010 Roland Garros winner Francesca Schiavone, Julien Benneteau, Gilles Muller, Florian Mayer and Anabel Medina Garrigues. | READ: Farewell, David Ferrer

September 1, 2018 - Nick Kyrgios in action against Roger Federer at the 2018 US Open. (USTA/Garrett Ellwood)
Photo by:  (USTA/Garrett Ellwood)

7) Nick Kyrgios is an enigma. His otherworldly talent in undeniable. The Aussie possesses a lethal arsenal that includes one of the whippiest, biggest forehands in the game, and a disarming serve that gets him plenty of free points. His contemporaries have long bellowed his praises. But Roger Federer might have put it best when he called Kyrgios an "unpredictable player who can just turn it on whenever he wants to." And therein lies the rub: it often appears that Kyrgios doesn’t want to flip that switch at all. Either way, fans are rooting for the 23-year-old to put it all together. Perhaps he should study the on- and off-court demeanor of Federer, the player who cut short his US Open stay in the third round. "I could take a leaf out of his book," said Kyrgios. "The way he behaves on court, his demeanor, I could definitely take away. I don't want to change myself too much, but I could definitely take away things he does in certain situations. He's the ultimate role model to anyone who wants to play."

play video Highlights: Rafael Nadal vs. Dominic Thiem - QF

8) The Nadal vs. Thiem five-setter was the stuff of legend. Dominic Thiem’s first set against Rafael Nadal in the quarterfinals — only the fourth time in his storied Grand Slam history that Rafa was blanked 6-0 — was arguably the most efficient, squeaky-clean set the sport has ever seen. A stroke-by-stroke study would be tantamount to The Anatomy of the Perfect Set. Even John McEnroe said, "It was the set you dream of, where everything works." All of which makes the Mallorcan Nadal’s five-set comeback more remarkable. The nearly five-hour-long quarterfinal, which stretched beyond 2 a.m., was without a doubt one of the most epic matches ever played on the grounds of the USTA Billie Jean King National Tennis Center. You can bet this one will be talked about for years to come. "It's cruel sometimes, tennis, because I think this match didn't really deserve a loser," said Thiem after the match. "But there has to be one."

9) Japan is a tennis powerhouse. For the first time ever, two Japanese players — Naomi Osaka and 2014 runner-up Kei Nishikori — reached the semis at a major. Osaka, of course, would go on to claim the final, becoming the first Japanese man or woman to win a Grand Slam singles title. | READ MORE: Looking for some good news, Japan turns to Nishikori and Osaka at US Open

September 9, 2018 - 2018 US Open Men's Singles Champion Novak Djokovic. (USTA/Garrett Ellwood)
Photo by:  (USTA/Garrett Ellwood)

10) Novak is back. To think that just a few months back, Novak Djokovic seemed a wayward soul, his once dominant form missing in action. In January, the Serb underwent a surgical procedure on his elbow. Retaking the court in Indian Wells in March, he looked lost in his opener against a 109th-ranked qualifier from Japan, Taro Daniel, falling, 6-3, 6-4. But just when we started to think the surefire Hall-of-Famer might be on his way out, Nole rediscovered his form, winning his 13th major at Wimbledon and following with the Cincinnati title, the last feather in his Career Golden Masters cap. And at the US Open, he swept past 2009 champion Juan Martin del Potro in straight sets to tie Pete Sampras for third place all-time on the Grand Slam singles titles list.

11) Bethanie Mattek-Sands is one tough cookie. We saw her crumble to the court in agony last year at Wimbledon, a horrifying knee injury summoning flashbacks of the Lawrence Taylor-Joe Theismann collision of 1985, when the Redskin quarterback saw his career come to an end with a compound leg fracture. Many doubted Bethanie Mattek-Sands would ever return to the court. But not the 33-year-old Arizonan. On Saturday at the US Open, she captured the mixed doubles title with Brit Jamie Murray. "Going from not being able to get myself out of bed last year to play in this final — I don’t care what anyone tells you; if you’re too old or you’re too young, you’re too big or you’re too small. You haven’t had enough opportunities or you’re still waiting for yours. You can do anything you put your mind to," she said, fighting back tears. "Go out there and choose your attitude. Choose happiness every day no matter what and big things will happen." | READ MORE: Mixed title caps Mattek-Sands comeback

12) There’s nothing quite like a ‘Tennis Mom.’ Serena wasn’t the only super mom in the 2018 main-draw singles/doubles. Among the other mothers in action on the courts of the USTA Billie Jean King National Tennis Center were Patty Schnyder, Vera Zvonareva, Kateryna Bondarenko, Tatjana Maria, Evgeniya Rodina, Marketa Vondrousova and Maria Jose Martinez Sanchez.

August 24, 2018 - Patty Schnyder in action against Jessica Pegula during qualifying at the 2018 US Open. (USTA/Darren Carroll)
Photo by:  (USTA/Darren Carroll)

13) Tennis is a sport for life. The US Open saw the crafty 39-year-old Swiss Patty Schnyder continue her comeback with a successful run through the qualifying draw. Joining the former world No. 7 in the qualifying rounds was 2010 US Open runner-up Vera Zvonareva, now 33. Like Schnyder, the Russian earned main-draw status, reaching the second round.

September 4, 2018 - Sloane Stephens in action against Anastasija Sevastova at the 2018 US Open. (USTA/Darren Carroll)
Photo by:  (USTA/Darren Carroll)

14) With a title defense comes pressure. As 2017 champ Sloane Stephens discovered, going back-to-back in New York can be a daunting task. From Day 1, it seemed the hard-hitting Floridian wrestled with the concept of defending her crown. "There’s a lot of stress, a lot of pressure. I'm just going to go out and handle it as best I can." But Stephens soon balked at the very idea of a title defense altogether, saying, "Defending a title isn't defending. If you were to play the same people in a row again and beat all of them again, that would be defending your title. When you're playing a whole new draw, different seedings, different ranking, there's so much that goes into it. When you go to a tournament, it starts all over again." Ironically, Stephens fell in a rematch of her ’17 quarterfinal against Anastasija Sevastova, losing 6-2, 6-3. | Stephens: 'On coaching, stick with what you know'

September 9, 2018 - 2018 US Open Women's Singles Champion Naomi Osaka. (USTA/Mike Lawrence)
Photo by:  (USTA/Mike Lawrence)

15) Naomi Osaka is one cool character. Naomi Osaka can come off as more Comic-Con fangirl than cutthroat tennis pro; shy and soft-spoken. But don’t be fooled: under extreme conditions in her first Grand Slam final, facing her childhood hero in match filled with a wide range of emotions, the 20-year-old didn’t flinch, kept her composure and closed out a 6-2, 6-4 triumph to signal the coming of a new generation.Open Interview: Naomi Osaka

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16) Althea Gibson’s legacy is an enduring one. It was announced that an interactive monument honoring Althea Gibson will be unveiled at the US Open in 2019, capturing the spirit of the iconic pioneer. Gibson was the first African-American player to break the color line in international tennis and, in 1956, became the first person of color to win a Grand Slam title.

17) The stars come out for the Open. Per usual, a plethora of A-listers were on-hand for the Flushing festivities, including Bill Clinton, Meryl Streep, Alec Baldwin, Jerry Seinfeld, Ben Stiller, John Hamm, Christie Brinkley, Spike Lee, Michael Keaton, Steve Kerr, Kevin Hart, Pierce Brosnan, Aziz Ansari, Dr. Oz, Adrian Brody, Peter Sarsgaard, Karlie Kloss, Carli Lloyd, Jimmy Buffett, Ashley Graham, Katie Ledecky, Alex Morgan, Clive Davis, Jason Collins, Adam Rippon, Priyanka Chopra, Nick Jonas, Adam Silver, David Fizdale, David Dinkins, Michael Bloomberg, Danai Gurira, Riz Ahmed, Steve Schirripa, D’Angelo Russell, Sandra Bernhard, Dierks Bentley and Ralph Macchio. | GALLERY: Celebs at the US Open

play video Highlights: Bryan and Sock vs Kubot and Melo

18) Mike Bryan is a winner, no matter whom he partners with. His twin brother Bob was sidelined with a hip injury. But that didn’t keep Mike Bryan from yet another hardware haul. The 40-year-old former Stanford standout won a record 18th Grand Slam doubles title, teaming up with fellow American Jack Sock to dismiss Kubot/Melo, 6-3, 6-1, in Arthur Ashe Stadium. For most of his career, Bryan had played with his sibling, winning 16 Grand Slam crowns to form one of the game’s most illustrious teams. Together they had won five US Open titles. Who will Mike play with in 2019? "I think Bob's got first dibs," he said.