BEIJING (AP) U.S. Open champion Flavia Pennetta struggled in her first match since winning her maiden Grand Slam, needing nearly 2 1/2 hours to beat Chinese wild card Han Xinyun 7-5, 4-6, 6-4 in the first round of the China Open on Sunday.
Top-seeded Simona Halep of Romania retired from her match against Spain's Lara Arruabarrena with a recurring Achilles injury while trailing 5-4 in the first set. It was one of four retirements among the women on the second day of the tournament.
''I thought that it's getting better and I can play,'' Halep said. ''But no. I don't want to force (it).''
Halep hopes to be fit in time to play the WTA Finals in Singapore in a few weeks.
''I need treatment and I need break, for sure,'' she said.
Fourth-seeded Agnieszka Radwanska advanced when Coco Vandeweghe quit after dropping the first set 6-3, and seventh-seeded Carla Suarez Navarro of Spain moved on when Lesia Tsurenko of Ukraine retired after also losing the first set 6-3.
Kazakhstan's Zarina Diyas also retired after dropping the first set against Puerto Rico's Monica Puig 6-4.
Defending champion Maria Sharapova withdrew before the tournament began with a left forearm injury that forced her to retire from her first-round match at the Wuhan Open last week. Top-ranked Serena Williams is also skipping the China Open and season-ending WTA Finals to rest and recover from injuries after falling just short in her bid to win the Grand Slam at last month's U.S. Open, losing to Roberta Vinci in the semifinals.
Han broke the third-seeded Pennetta early in the third set to take a 2-0 lead, but the Italian rallied to win six of the next eight games to close out the match. Pennetta had 41 winners to 35 unforced errors and broke Han's serve eight times.
Pennetta rose to a career high No. 6 in the world after defeating Vinci to win the U.S. Open last month when she announced her retirement at the end of the season.
Also, Sara Errani of Italy upset second-seeded Petra Kvitova 7-5, 6-4 and Sloane Stephens of the United States defeated ninth-seeded Karolina Pliskova of the Czech Republic 6-3, 6-2.
Kvitova reached the final of the China Open last year, losing to Sharapova, but couldn't get past the first hurdle this time around. She only converted four of 17 break points and dropped her own serve six times.
''It was the kind of game which I really had to be ready physically and mentally and everything, and I just wasn't,'' Kvitova said. ''I'm kind of sleepy all day long. It's just weird.''
In the men's draw at the China Open, No. 1 Novak Djokovic is competing for the first time since winning his 10th major title at the U.S. Open. He typically plays some of his best tennis during the late-season Asian swing, capturing the China Open title five of the past six years and the Shanghai Masters in two of the past three years.
''The record that I have in these tournaments in China gives me a lot of obvious motivation to come back,'' he said Sunday.
''It's been a long season, no question about it, a lot of matches played,'' Djokovic said. ''People are asking me if maybe it's smarter to skip this Asian swing so I can be well-rested for Europe and for (ATP) World Tour Finals because I've played much. But I don't feel like that's the right decision to do.''
Rafael Nadal, who has dipped to No. 7 in the rankings, will be looking to end his disappointing season with a strong showing in Beijing and next week's Shanghai Masters.
''I don't feel that I am suffering on court as I did the first six, seven months of the season,'' he said Sunday. ''I feel that I am more under control of my emotions on court. So that's a very big advance for me.''