The three-time major champion Maria Sharapova

Maria Sharapova’s slow start almost turned into an early exit at the U.S. Open.

The three-time major champion picked up her game in time to avoid an upset against 102nd-ranked Heather Watson, rallying for a 3-6, 7-5, 6-3 victory Monday in the opening round.

After being thoroughly outplayed in the first set, third-seeded Sharapova let a 4-1 lead in the second slip, as well. She shored things up at 5-all in the second to pull out that set. She also led 4-1 in the third, but gave back a break. After that, Sharapova broke right back then served out her match against the 19-year-old Brit, who was making her first appearance in the main draw at Flushing Meadows.

Sharapova improved to 12-0 this year in third sets.

“In the end, that’s kind of where it counts,” she said after a match that lasted 2 hours, 34 minutes. “No matter how tired or whether you’re playing your best tennis or sometimes your worst, you keep fighting for it.”

Not showing the same kind of fight was fifth-seeded Petra Kvitova, who became the first reigning Wimbledon champion to lose in the first round of the U.S. Open. She made 52 unforced errors in a 7-6 (3), 6-3 loss to Alexandra Dulgheru and has won only two matches since hoisting the trophy at the All-England Club last month.

“After I made some mistakes, I was mentally down,” Kvitova said.

Last year’s U.S. Open and Wimbledon runner-up, second-seeded Vera Zvonareva, defeated Stephanie Foretz Gacon of France, 6-3, 6-0.

Other women’s winners included No. 13 Peng Shuai, No. 19 Julia Goerges and No. 27 Lucie Safarova.

But Sharapova-Watson was the best match of the afternoon.

With Watson nimbly covering a court that players say is playing slower than usual this year, Sharapova had to fight, and the match turned into a showdown of styles — the Russian’s punishing, aggressive baseline game vs. Watson’s grinding, retrieving relentlessness. The final stats were no surprise: Sharapova finished with 41 winners and 58 unforced errors, compared to nine winners and 30 unforced errors for her opponent.

“There’s no doubt that she’s a great up-and-coming player who showed some of her best tennis today,” Sharapova said. “She played really smart in the first. I was making too many errors. Consistency at the end helped me get through the match.”

The early headliner for the men was American Mardy Fish, who at No. 8 is the highest-ranked U.S. player in the tournament.

Fish lived up to his billing, opening his stay at Flushing Meadows with a 6-2, 6-2, 6-1 victory over Tobias Kamke of Germany.