Former world No 1 Caroline Wozniacki, one point from falling behind 5-0 in the opening set, rallied to upset ninth-seeded Russian Svetlana Kuznetsova in straight sets at the US Open on Wednesday.
The unseeded Dane, slowed by injuries this season, took advantage of some sloppy play by the former US Open champion to post a 6-4 6-4 victory and advance to the third round.
"It was not looking good for me," Wozniacki said on the Arthur Ashe Stadium court after the match.
"I've been in this situation before. I was down 6-1 (actually 6-2), 4-1 (in the fourth round in 2009) to her once on this court I said 'I can do this, I can pull this through.' And I won last time and I won today and I'm really proud of that."
Wozniacki, twice a US Open runner-up, has struggled through ankle and arm injuries this season and came to Flushing Meadows ranked 74th in the world.
"I stopped looking at the ranking once I fell out of the top 10," said 26-year-old Wozniacki, who has endured a couple of down years. "I feel like I belong at the top.
"Today I beat someone who's been playing really well this year and that's definitely going to build my confidence."
Wozniacki, one of the game's top retrievers, showed no injury effects as she dashed around the court to extend rallies.
Kuznetsova, the 2004 US Open winner, who won at Sydney this season and reached the fourth round at both the French Open and Wimbledon, blamed herself.
"After 4-0 (in the first set) it was very even games, even on my serve," said the Russian. "Then I made a couple of unforced errors which I shouldn't do and I just let her in the match. And she started to believe.
"I was really frustrated because I felt like I was playing good, just didn't close a few balls at the net.
"The second set I tried to hang in there, but a few unforced errors," added 31-year-old Kuznetsova, who registered 31 errors in the one hour, 44 minute match.
The win gave Wozniacki a 7-6 edge in career matches against Kuznetsova, who had beaten the Dane in the first round of Wimbledon this year.
Next up for Wozniacki is Romanian Monica Niculescu, a 6-0 6-1 winner against compatriot Ana Bogdan.