Peng Shuai knows how to work up an appetite.

After her marathon victory over defending champion Petra Kvitova at the Wuhan Open on Monday, Chinese No 1 Peng said her immediate priority was to "eat a lot of good food."

Peng finally nailed down the 7-6 (7), 6-7 (5) and 7-6 (3) triumph in three hours and 34 minutes.

"I didn't realize how long the match was," she told China Daily.

"For a long time, I haven't played many matches that had so many tie-breaks. It might be the first or second time."

Peng reached a career-high ranking of world No 1 in doubles in February 2014, making her the first Chinese player to achieve that status.

She won a gold medal at the 2010 Asian Games, and won her first doubles championship at Wimbledon in 2013.

Her second doubles title came at the 2014 French Open.

Kvitova didn't anticipate playing for so long on Monday, either.

"It's always more difficult to play someone in their home country, but I heard my fans too, so it was nice that they cheered for me," said the 27-year-old Czech.

"It's probably the longest match I've ever played, and it was really up and down. I probably should have taken the first set tie-break after leading 6-3.

"Still, I fought really hard from 5-3 down in the third. In the end, my opponent was just a little bit luckier.

"I was cramping at the end so it was pretty challenging for me, so in one way I'm pretty proud of myself that I was able to fight so hard.

"I hadn't practiced too much before this tournament but I played a lot today. I'm not usually a player who gets into such long matches."

Kvitova, No 14 in the world, has 20 career singles titles, including two championships at Wuhan in 2014 and 2016. The 31-year-old Peng, ranked No 24, said she went into the match hoping "not to lose too easily."

"I never beat her. At the 2012 Olympics, I remember that I had a chance to beat her but didn't make it. She attacks really early, has a big serve and is so powerful," Peng said.

"She is a very good player, very powerful. She attacked the ball very early. And then I just tried to fight and play some good matches. Not to lose too easily - that was what I was thinking early on. I just told myself to fight point by point, and in the end I think I played very well."

Peng sustained a serious back injury that forced her out of the 2015 season, but she's now back on track to regain her world rankings.

"A year ago I could only sit and watch because my back was injured," she said. "But this time, I can play and fight and tell myself to enjoy it."

Kvitova's defeat continued a trend of major upsets after US Open champion Sloane Stephens and fifth seed Johanna Konta were also eliminated on Monday.

Wang Qiang, China's world No 55, knocked off Stephens while Konta, who was handed a bye as the fifth seed, failed to get on the scoreboard against world No 37 Ashleigh Barty of Australia in the first set and eventually succumbed 6-0, 4-6, 7-6.

"I didn't play a great match, but my opponent played very well," Stephens said. "I mean, it's difficult. It's the end of the year. Even though I played five tournaments, I feel like I played 25. There's some fatigue, for sure."

In second-round play on Tuesday, Wang defeated Romania's Sorana Cirstea 6-3, 6-3.

Meanwhile, No 26 Zhang Shuai claimed a 7-5, 5-7, 6-1 opening-round victory over Croatia's Donna Vekic, but came up short against world No 4 Karolina Pliskova of the Czech Republic in Tuesday's second round, losing 6-4, 3-6, 6-4.

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