WIMBLEDON, England - On the verge of victory, Maria Sharapova briefly lost her bearings.

Sharapova's old serving problems resurfaced Thursday at Wimbledon, costing her the second set before she recovered to beat dangerous Tsvetana Pironkova, 7-6 (3), 6-7 (3), 6-0.

The Court 1 match took two days and ended three minutes after Serena Williams concluded her second-round victory on Centre Court, beating qualifier Melinda Czink 6-1, 6-4.

It was a good day for Americans, as No. 28-seeded Christina McHale and Varvara Lepchenko also advanced.

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The No. 1-ranked Sharapova saved five set points in the first set and led the second set 3-1 when play was halted Wednesday because of darkness. She lost the first two games when the match resumed, and double-faulted on her first three service points in the tiebreaker.

"It felt like two matches in a way," Sharapova said. "Today I wanted to start off really well because I knew I was up a break. Didn't go according to plan. Really served sloppy."

Sharapova underwent shoulder surgery in 2008 and has been prone to double-faults, but in the final set she had no trouble with her serve — or anything else. She won 21 of the last 27 points and finished with just 11 unforced errors.

Sharapova said she didn't make any major changes down the stretch.

"We were playing with the same balls; I played with the same racket," she said. "I just started doing things a little bit better."

Pironkova, ranked 38th, beat Venus Williams at Wimbledon each of the past two years,

"If she played on grass 365 days a year, she'd be top five probably," Sharapova said. "She has the perfect game for it."

But Sharapova's at her best in winner-take-all sets. She improved her record in three-set matches to 9-0 this year and 21-1 since the beginning of 2011.

She has won 14 consecutive matches, including the French Open this month to complete a career Grand Slam.

While Sharapova battled an erratic serve, with eight aces and 10 double-faults, four-time champion Serena Williams had no such trouble. She won 27 of 28 points on her first serve, including 10 aces, and never faced a break point. Czink twice whiffed on returns.

"I love my serve," Williams said, "and I love feeling good when I serve."

The sixth-seeded Williams could meet Sharapova in the final next week. A 17-year-old Sharapova defeated Williams for the Wimbledon title in 2004.

Defending champion Petra Kvitova, seeded fourth, advanced by beating Elena Baltacha of Britain 6-0, 6-4.

The 20-year-old McHale advanced to the third round at her fourth consecutive Grand Slam tournament when she beat Mathilde Johansson 7-5, 7-5. McHale next plays No. 8-seeded Kerber with a chance to reach the fourth round at a major for the first time.

"I am still not finding my best tennis consistently over the two matches I have played," McHale said. "I still feel I can be a lot more offensive."

Lepchenko, ranked 53rd, advanced to the third round at Wimbledon for the first time by beating No. 31 Anastasia Pavlyuchenkova 7-6 (4), 6-4.

No. 2-seeded Victoria Azarenka defeated Romina Oprandi 6-2, 6-0.

Sara Errani committed only five unforced errors and beat Anne Keothavong of Britain 6-1, 6-1. The 25-year-old Errani, an Italian who has blossomed in Grand Slam competition this year, matched her best Wimbledon showing by advancing to the third round.

She was the French Open runner-up this month to Sharapova, and she's 12-2 in major tournaments in 2012. She began this year with a career record of 15-17 at majors.

Playing the day's first match on Court 2, the 10th-seeded Errani erased all three break points she faced and won in 61 minutes. That was a grueling effort compared with Wednesday, when she played only one point to complete a victory suspended overnight because of rain.