With only Day 1 in the books, the 2018 US Open has already produced its fair share of highlights. A record 67,832 fans took in a total of 64 singles matches at the USTA Billie Jean King National Tennis Center, as half of both the men’s and women’s fields were in action.

Here’s a recap of the day’s top stories.

Kaia Kanepi stuns Simona Halep in Armstrong opener: In the first main-draw match played on the new Louis Armstrong Stadium, former world No. 15 Kaia Kanepi delivered the shock of the day by blasting her way past world No. 1 and reigning French Open champion Simona Halep. The Estonian gained control early, winning five of the match’s first six games, and remained in command throughout, firing 26 winners in the 6-2, 6-4 upset.

Serena makes winning comeback: Playing her first US Open as a new mom, Serena Williams returned with an emphatic 6-4, 6-0 victory over Poland’s Magda Linette in Arthur Ashe Stadium. The six-time US Open champion, who played just three matches on the North American hard-court swing this summer, was able to raise her game on the New York stage and move within one match of a potential third-round showdown with sister Venus, who advanced in three sets against Svetlana Kuznetsova in a first-round battle of former US Open champions.

David Ferrer’s Grand Slam career ends with retirement against Rafael NadalThe all-Spanish battle ended with a warm embrace at the net after Ferrer was forced to retire midway through the second set in the Arthur Ashe Stadium nightcap. The 36-year-old, who reached the semifinals in New York in 2007 and 2012, announced that the US Open would be the final Grand Slam of his 18-year professional career. Similarly, Germany’s Florian Mayer saw his career come to a close on Day 1, with a four-set defeat to Croatia’s Borna Coric.

Kevin Anderson survives five-set thriller: The 2017 finalist found himself trailing American Ryan Harrison by two sets to one on Court 17, fighting for his tournament life against not only Harrison, but also cramps and a pro-American crowd. The South African, who squandered four set points in the second set, dug deep to make sure he was still standing tall after four hours, 14 minutes.

play video AI Match Highlight: Stephens vs. Rodina - Round 1

Seven former champs advance: Seven of the eight former US Open champions in action on Day 1 advanced, including defending champs Rafael Nadal and Sloane Stephens, both Williams sisters, Juan Martin del Potro, Andy Murray, and Stan Wawrinka. Kuznetsova, who was turned back by Venus Williams, was the only champ to fall.

On Day 2, the theme of former champions continues, as six former trophy-winners highlight the day's play. Novak Djokovic, Roger Federer, Marin Cilic, Angelique Kerber, Maria Sharapova and Sam Stosur will all be in action, with Stosur taking on No. 2-seeded Caroline Wozniacki in the Arthur Ashe Stadium opener. 

2017 finalist Madison Keys will follow Federer in the Ashe evening twin bill, while another American, Danielle Collins, takes on US Open Series Breakout Performer and Connecticut Open champion Aryna Sabalenka in a battle of rising stars on Court 5. Closing out the night session on the new Louis Armstrong Stadium will be world No. 4 Alexander Zverev.