WHAT HAPPENED: Into the second week of the US Open for the third time in five years, 2014 runner-up Kei Nishikori advanced to the Round of 16 on Saturday with a 6-4, 6-4, 5-7, 6-1 upset of 13th-seeded Argentine Diego Schwartzman.

It’s hard to believe that it’s been four years since Nishikori reached the final in Flushing Meadows. It’s been a rough go for the Japanese superstar since that breakthrough. After rising to a career-high No. 4 in the world in 2015, he has struggled with a variety of injuries. Wrist woes sidelined him for half of the 2017 season, including the US Open, and the Michael Chang-coached Nishikori subsequently dropped out of the Top 20. Earlier this year, he fell to No. 39, his lowest standing since 2011. But as he showed on Day 6 on the Grandstand, Nishikori’s game may be coming together at the right time.

“It hasn’t been easy, especially after coming back from an injury,” said Nishikori, who overcame 63 unforced errors in the three-hour, 17-minute contest. “In the beginning, I was playing Challengers. But I’m happy with my level again.”

play video AI Match Highlight: Schwartzman vs. Nishikori - Round 3

Schwartzman certainly had his chances in the opening set. He surged ahead 3-0 with an early break, but dropped six of the next seven games to surrender the stanza. Leveled at four games apiece in the second and serving at 30-40, Schwartzman scooped a forehand into the net to hand his 28-year-old opponent another break, falling behind two sets to love.

As he did in the opening set, Schwartzman surged ahead 3-0 in the third. But an ill-timed double fault (one of nine on the day) from the 26-year-old at 4-2 would bring the set back on serve. Nishikori later saved a pair of set points serving at 4-5, but couldn’t save a third at 5-6.

Nishikori would convert breaks in the first, fifth and seventh games of the fourth set to put the match away for good.   

Despite Schwartzman’s defeat, the shortest man in the Emirates ATP Rankings is a player on the rise. In 2017, the 5-foot-7 baseliner broke through to a career-high ranking on nine occasions. This year, he’s done that a career-high eight times, peaking at No. 11 in June. At 26, El Peque ("Shorty"), as he is known among his countrymen, is standing tall. Against Nishikori, however, one glaring stat hurt him most: The 21 break points he faced. He managed to fight off 13, but it wasn’t enough.  

WHAT IT MEANS: Nishikori is headed for a Round of 16 matchup with veteran Philipp Kohlschreiber, a 6-7, 6-4, 6-1, 6-3 upset winner over No. 4 seed Alexander Zverev. Nishikori is unbeaten against the German in two previous encounters, including a 6-1, 6-2 decision in the fourth round of the Rome Masters earlier this year. “Philipp is a great friend, good player. Very talented. Big backhand,” said Nishikori. “It won’t be easy

MATCH POINT: Nishikori improved to 3-0 in head-to-heads with Schwartzman, having twice defeated the Argentine in 2017 (Buenos Aires, Madrid).