China’s Peng Shuai returns to Agnieszka Radwanska of Poland during their second round match in US Open. (Source: Reuters)

Chinese doubles specialist Peng Shuai supplied a shocking start to the second round of the U.S. Open by upsetting fourth-seeded Agnieszka Radwanska of Poland 6-3 6-4 on a hot, humid Wednesday at Flushing Meadows.

The doubles world number one used piercing, two-fisted groundstrokes to put Radwanska on the defensive and claimed the biggest scalp of the tournament so far on her third match point with a backhand crosscourt winner that brushed the corner lines.

Radwanska, winner in the Montreal hardcourt run-up to the U.S. Open and a semi-finalist at this year’s Australian Open, saved a match point in the ninth game to hold serve for 5-4 and fended off another in the next game before Peng’s last winner.

The 28-year-old Peng, the French Open doubles champion and 2013 Wimbledon doubles winner who is seeking her first career WTA Tour singles title, registered 28 winners in the 96-minute match at Louis Armstrong Stadium.

“I had two match points and didn’t make it,” Peng said in an oncourt interview about two backhand errors that prolonged the match.

“But I just said ‘fight, fight’ and it’s an amazing time for me,” added Peng, who has 16 career doubles wins and in February became the first Chinese player to become a world number one in tennis.

The Chinese, who entered the contest 3-22 lifetime against top-five opponents, was masterful in turning points of the match. Peng won three of five break points against Radwanska, who succeeded only once in seven opportunities to break.

She has six career singles runner-up finishes, including this year in Shenzhen, and will be aiming to improve on her best grand slam singles result, having reached the fourth round four times, including at this year’s Wimbledon.

“I still have a lot to learn,” Peng said. “I will try to keep on fighting. I still have to working hard, keep going and fighting and improve my tennis.”

Peng, ranked 39th in singles, will play 28th seed Roberta Vinci in third round. The Italian advanced with a 2-6 6-4 6-1 win against Irina Camelia Begu of Romania.

Johanna Larsson of Sweden eliminated another seed with a 5-7 6-4 6-2 upset of 21st-seeded American Sloane Stephens, a 2013 Australian Open semi-finalist.

Also advancing to the third round was 22nd seed Alize Cornet of France, a 6-3 6-3 winner over 37th-ranked Daniela Hantuchova of Slovakia.

In later action, sixth-seeded Tomas Berdych of the Czech Republic will meet former champion Lleyton Hewitt of Australia in a first-round match, and French Open champion Maria Sharapova will meet Alexandra Dulgheru of Romania in second-round play.

The night session will feature seven-times grand slam singles winner Venus Williams against Swiss Timea Bacsinszky, and Australian Open champion Stan Wawrinka of Switzerland in a second-round match against Brazilian Thomaz Bellucci.

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 had her earliest loss at the U.S. Open, upset in the second round Wednesday by 96th-ranked Johanna Larsson.

Down a set and a break, Larsson rallied to win 5-7, 6-4, 6-2 to match her best performance at a major tournament. The 26-year-old Swede had been 0-4 at Flushing Meadows before this year.

When the match ended with her 63rd unforced error, the 21st-seeded Stephens 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 has slid to No. 24 in the rankings.

“Everyone goes through times like this,” she said. “I’m not the first person and won’t be the last.”

Larsson has now reached the third round at a major tournament twice this year after breaking through at the French Open.

“I just was trying to really tell myself to go for it,” she said. “You won’t win matches by holding back. Also, a lucky shot every here and there.”

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.

The 39th-ranked Peng won 6-3, 6-4, giving China a big win in the tournament with third-ranked Li Na out with a knee injury.

“It’s an amazing time for me,” Peng said.

The U.S. Open is the only Grand Slam tournament in which Radwanska, the 2012 Wimbledon runner-up, has failed to reach the quarterfinals.

“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 coming in 2011. That year was also the last time the 28-year-old made the third round at the U.S. Open.

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.

(AP)