NEW YORK (AP) -- Once a sure bet to stick around for a while at Grand Slam tournaments, Sloane Stephens suddenly can't even win there.
The 21-year-old American stumbled to her earliest loss at the U.S. Open, upset in the second round Wednesday by 96th-ranked Johanna Larsson.
''Everyone goes through times like this,'' said Stephens, who was seeded 21st. ''I'm not the first person and won't be the last.''
Down a set and a break, Larsson rallied to win 5-7, 6-4, 6-2 to equal her best performance at a major tournament. The 26-year-old Swede had been 0-4 at Flushing Meadows before this year.
''I shouted 'Come on' a few times, not so much for myself but also to show her that I'm still here to win it,'' Larsson said. ''I know, myself, that when you have an opponent who is fighting to the last point, it is very difficult.''
Her victory was the second big women's upset of the day. Peng Shuai beat fourth-seeded Agnieszka Radwanska, the first top-10 player knocked out of the tournament.
When Stephens' match ended with her 63rd unforced error, she was in such a hurry to leave Arthur Ashe Stadium that she briskly walked around the net to Larsson's side of the court for the handshake.
As Stephens had climbed the rankings, the knock on her was that she would shine in the big-time tournaments and slump in other events: Her Grand Slam record coming into Wimbledon this year was 32-12, while she's 58-57 everywhere else.
Stephens reached at least the fourth round at six straight major tournaments starting with the 2013 Australian Open, when she stunned Serena Williams to make the semifinals. The longest active streak at the time, it ended with a first-round loss at Wimbledon this summer.
Now her stay at her home Grand Slam event is over quickly after she had advanced to at least the third round in three previous trips to the U.S. Open.
On the verge of breaking into the top 10 last fall, Stephens' ranking has slid to No. 24.
''Think about this as a little speed bump and work through it and I will get better,'' she said.
Larsson has now reached the third round at a major tournament twice this year after breaking through at the French Open.
''That was like a kick in the bum that I can do well and really beat the best players,'' she said.
The 39th-ranked Peng won 6-3, 6-4, giving China a big win in the U.S. Open with third-ranked Li Na out with a knee injury.
Peng said it's simpler when Li is around to soak up all the attention.
''They didn't watch me too much because there is more pressure,'' she said. ''Not easy to handle that.''
The U.S. Open is the only Grand Slam tournament in which Radwanska, the 2012 Wimbledon runner-up, has failed to reach the quarterfinals. In 2010, it was Peng who also knocked her out in the second round, the Chinese veteran's only win in four previous meetings.
''I really want to know the answer,'' Radwanska said. ''Then maybe I will find a way to play better here and just try another way to be in the second week.''
Peng had been 3-22 against top-five opponents, the last victory in 2011. But she was coming off a fourth-round showing at Wimbledon, equaling her longest run at a major tournament.
On Wednesday, she won a 27-point rally with a sizzling backhand winner down the line to set up her third match point, then clinched victory with another backhand winner deep into the corner.
Peng said she reminded herself: ''I still have to go for my shot because this is my weapon.''