WHAT HAPPENED: On Wednesday night, world No. 1 Iga Swiatek won just her second match in Arthur Ashe Stadium to advance to her first US Open semifinal.

The 21-year-old from Poland knocked out No. 8 seed Jessica Pegula, the last American standing in the women's singles draw, 6-3, 7-6(4). A gritty Pegula twice denied Swiatek from serving out the match, but the top seed did just enough in the tiebreak, firing three winners to escape in straights after one hour, 53 minutes.

The back-and-forth second set saw 10 breaks in its 12 games, with a combined 17 break points.

"She's a great player," Swiatek said of her opponent. "I was trying to push her back, but she's really good at receiving so she put pressure on me. That's why it ended up in a tiebreaker."he Stadium nightcap.

MATCH POINT: Prior to Swiatek, the last US Open No. 1 seed to reach the semifinals was none other than Serena Williams in 2016. Williams was also the last No. 1 seed to win the New York title, in 2014.