China's Peng Shuai put a stop to Agnieszka Radwanska's bid to reverse her US Open fortunes on Wednesday, toppling the fourth seed in three sets to reach the third round.
Poland's Radwanska, a former Wimbledon finalist who counts this year's Australian Open among two other Grand Slam semi-final appearances, had hoped to make it past the fourth round at Flushing Meadows in her ninth attempt.
But the 39th-ranked Peng had other ideas, breaking Radwanska three times en route to a victory sealed with a backhand winner on her third match point -- her 28th winner of the contest.
"She's tough to play," said Peng, who beat Radwanska at the same stage of the US Open in 2010.
Peng thought that coincidence might be a lucky talisman, but her biggest memory of playing Radwanska was a 2011 Australian Open loss in which she squandered two match points.
"I kept running, I fought. It was amazing. I will try to keep going," Peng said.
Radwanska, meanwhile, couldn't put her finger on her US Open trouble.
"I really want to know the answer, then maybe I will find a way to play better here and just try another way to be in the second week," she said.
With two-time defending champion Serena Williams taking the day off, French Open finalists Maria Sharapova and Simona Halep, and seven-time Grand Slam champion Venus Williams headlined women's second-round action.
Fifth-seeded Sharapova, who lifted a fifth career Grand Slam trophy at Roland Garros, was to take on Alexandra Dulgheru, the Romanian world number 95.
World number two Halep, seeded second behind two-time defending champion Serena Williams, needed less than an hour to advance with a 6-2, 6-1 victory over Slovakian Jana Cepelova.
Halep was broken early to trail 0-2, but won 12 of the next 13 games to secure the win.
Sweden's Johanna Larsson and Swiss teen Belinda Bencic sprung minor upsets. Larsson rallied to beat 21st-seeded American Sloane Stephens 5-7, 6-4, 6-2 while 17-year-old Bencic, ranked 58th in the world, joined the youth movement spearheaded by 15-year-old CiCi Bellis by ousting Japanese 31 seed Kurumi Nara 6-4, 4-6, 6-1.
Sixth-seeded German Angelique Kerber advanced on cue, downing Russian Alla Kudryavtseva 6-2, 6-4 in a match that saw seven breaks of serve, and French 22nd seed Alize Cornet defeated Slovakia's Daniela Hantuchova 6-3, 6-3,
The biggest names of the men's field -- Novak Djokovic, Roger Federer and Andy Murray also had Wednesday off.
Australian Open winner Stan Wawrinka, the third seed from Switzerland, headlined the night session, taking on Brazil's Thomaz Bellucci in one of two men's second-round matches on the slate.
Wawrinka's triumph in Melbourne broke a streak of 16 straight Grand Slam titles won by tennis' Big Four of Rafael Nadal, Djokovic, Federer and Murray.
That major breakthrough was followed by a first-round exit at the French Open and a first quarter-final appearance at Wimbledon.
Sixth-seeded Czech Tomas Berdych brought Lleyton Hewitt's 62nd Grand Slam appearance to a quick end, downing the former world number one, and 2001 champion, 6-3, 6-4, 6-3 to reach the second round.
The 33-year-old Hewitt, who has had five surgeries in five years to keep his career going, had early breaks in both the second and third sets, but couldn't deny Berdych a 100th career Grand Slam match win.
Berdych became the ninth active men's player to reach the milestone -- an exclusive club that naturally includes Hewitt himself.
Croatia's 14th seed Marin Cilic, who reached his first Grand Slam quarter-final at Wimbledon, reached the second round with a truncated victory over Cypriot Marcos Baghdatis, the 2006 Australian Open finalist who was trailing 6-3, 3-1 in their match when he retired.
Spanish 19th seed Feliciano Lopez advanced when Croatian Ivan Dodig retired with their match knotted a 1-1 in the fifth set.
Dodig also retired at both the Australian and French Opens, and was a no-show at Wimbledon due to injury.
Seventh-seeded Bulgarian Grigor Dimitrov, trying to win his first US Open match after first-round exits the past three years, takes on US wildcard Ryan Harrison.