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.

The 29-year-old from Los Angeles opened the match by losing his serve, but that turned out to be the only hiccup. He is one of 14 American men entered in the U.S. Open, as the host country continues the quest to find its next great champion. No U.S. man has won a major since Andy Roddick won in New York in 2003.

"Andy's been the No. 1 player in our generation for years," Fish said. "This is extremely different for me, this feeling coming out here and trying to show everything you can, to show you're the No. 1 guy, at least for this tournament. It's been a lot of fun."

Also winning in early play Monday was 27th-seeded Marin Cilic, who defeated 19-year-old American Ryan Harrison 6-2, 7-5, 7-6 (6). Harrison, who made headlines last year with his first-round upset of 15th-seeded Ivan Ljubicic, had chances to serve out the second and third sets, but was broken each time.

He also squandered a 4-1 lead in the third-set tiebreaker — and took nothing away from this match but a few scratched-up rackets, the result of the multiple times he bounced them, kicked them and skidded them along the ground at Louis Armstrong Stadium. He also kicked a ball into the stands.

"I didn't break any rackets; I didn't say swear words on court," Harrison said. "It could have gotten better and I could have been better. I didn't really go nuts."

Other early winners included ninth-seeded Tomas Berdych, 20th-seeded Janko Tipsarevic, No. 31 Marcel Granollers, No. 22 Alexandr Dolgopolov and No. 13 Richard Gasquet.

No. 3 Roger Federer and Venus Williams — unseeded after missing time with injuries and illness — were scheduled for night matches.

Sharapova, meanwhile, was due for a rest after her longer-than-expected grind.

"I knew I wasn't playing my best tennis," she said. "I think the goal sometimes on this is just to get through it and keep waiting for that opportunity."