Maria Sharapova's stomach ache turned out to be nothing more than that.

That lopsided loss she suffered at the Olympics — well, that may have only been a false alarm, as well.

Playing her first match since a blowout loss to Serena Williams in London and a stomach virus forced her out of two tuneup tournaments, Sharapova returned to tennis in fine fashion Monday at the U.S. Open.

The third-seeded Russian came back from a three-week break and defeated Melinda Czink of Hungary 6-2, 6-2 in a stress-free, 67-minute first-round match at blustery Arthur Ashe Stadium.

Later, top-seeded Roger Federer took center stage and beat American Donald Young 6-3, 6-2, 6-4 to begin the chase for his 18th major title.

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Sharapova completed the career Grand Slam earlier this year by winning the French Open. Monday's victory, in front of the half-filled stadium, was her first match since a 6-0, 6-1 loss to Williams at the London Games in a gold-medal showdown that looked more like one of these first-round wipeouts Sharapova usually inflicts.

Turns out, Sharapova was dealing with some stomach pain then, which only got worse a few weeks later. She went to the doctor for a series of tests, including an ultrasound to see if she was pregnant. The test turned up negative.

"Just because of the pain I was having, it was really weird," said Sharapova, who is engaged to basketball player Sasha Vujacic. "They told me I was fine, not pregnant. Then, I'm like, 'Can I get my money back?'"

It has been an eventful summer for one of tennis' biggest stars.

After serving as the flag-bearer for Russia, then finishing as the silver medalist at the Olympics at Wimbledon, Sharapova's original plan was to come to North America and play in tuneups in Montreal and Cincinnati to acclimate herself to the hard courts.

But the Olympics took a lot out of Sharapova, and when she arrived in Canada, she got knocked down by a stomach ache so bad that she went to the doctor.

It turned out to be a virus — her body's way of telling her to take it easy, she said, so she withdrew from the events and took a few weeks off.

"It was a nice break in a way, but after so many weeks of practicing, you're just eager to get back on the court," she said.

She looked eager to get off the court, as well, showing very few signs of rust against her 88th-ranked opponent.

Wearing a soft-pink dress with a touch of mauve — more subdued than what she usually wears for, say, a nighttime appearance — Sharapova served five aces and maxed out at 115 mph. It took her 31 minutes to finish the first set and she was up 3-0 in the second before Czink got her only break.

That made things only mildly interesting, and only for a very short time. Leading 4-2, Sharapova won one point by chasing a ball almost into the stands on the sidelines, reaching out to get it back, then closing in on the net to win the point. Czink stood there shaking her head, hardly believing what she had just seen.

Sharapova said getting the blowout loss to Williams out of her mind was not a problem.

"It doesn't stick with you," she said. "I mean, personally, I've been part of many different types of matches in my career. Looking back at that week, it was really special. It was so hectic."

The routine win was part of a day filled mostly with by-the-book results: Defending champion Sam Stosur's 6-1, 6-1 victory over Croatia's Petra Martic, No. 3 Andy Murray's 6-2, 6-4, 6-1 win over Alex Bogomolov Jr., of Russia and, of course, a two-hour rain delay at a tournament that has finished on a Monday for four straight years because of bad weather.

Federer closed the night with a 1-hour, 34-minute dispatching of Young and stayed in the mix for his sixth U.S. Open title. Federer, a loser to Novak Djokovic in the semifinals the last two years, is seeded first for the 23rd time at a Grand Slam, breaking the record he shared with Pete Sampras.

"Being back in New York as world No. 1, it's crazy, and I really, really enjoy it," Federer said.

Before Federer played, No. 23 Kim Clijsters extended her Flushing Meadows winning streak to 22 straight matches, defeating the youngest player in the field, 16-year-old American Victoria Duval, 6-3, 6-1.

Top-seeded Victoria Azarenka, the Australian Open champion, began the quest for her second Grand Slam title of the year with a 6-0, 6-1 win over Alexandra Panova.

Stosur won the day's first match in Ashe, and any thought that the early round jitters might get to her — the way they did in first-round exits at the Australian Open and the Olympics or a second-round loss at Wimbledon — were over before the crowd even got settled.

The seventh-seeded Aussie won the first 19 points — she was five away from a perfect set before she double-faulted — and needed only 51 minutes to finish the match.

"It did pop into my head for a split second," Stosur said of the prospect of a golden set. "Then I hit the double fault and it was erased and I was quickly on with the next point."

Murray is trying to become the first man to win the Olympics and the U.S. Open in the same year. His first match of 2012 at Flushing Meadows gave him a decent test — with just a little something to worry about.

He fell down a break to open the first two sets but won the last five games of the first and last four games of the second, then cruised in the third, which he began by shouting "focus."

"It's an important stage of the match, when he was up 4-3 in the second with a break, then I won three games in a row and momentum was with me," Murray said. "You want to win the matches as quickly as possible."

He finished with 46 winners to 24 for Bogomolov, and handled the array of drop shots Bogomolov tried on him. Leading 4-1 in the third set, Murray grabbed his left hamstring while lunging for a ball near the net. But he closed out the match with no problem.

"Maybe I didn't take enough fluid," Murray said.

That could have been the problem No. 22 Florian Mayer encountered, as well. He withdrew while trailing 19-year-old American wild card Jack Sock 6-3, 6-2, 3-2, saying he felt dizzy and had blurred vision.

"He played the perfect match," Mayer said. "He hit the forehand fast, didn't really make any mistakes, just played really good."

Sock advanced to the second round for the second straight year. He'll be joined by Americans James Blake, a four-set winner over Lukas Lacko of Slovakia, 23rd-seeded Mardy Fish, who beat Go Soeda of Japan in three sets, and Tim Smyczek, who won 1-6, 6-4, 6-2, 4-6, 6-4 over Bobby Reynolds in a 3-hour, 33-minute, all-American matchup between qualifiers.

"It's obviously the biggest tournament for us Americans but I'm just trying to go about my business and treat it like any other week," said Smyczek, ranked 179th, after recording his first victory in a Grand Slam tournament.

Other winners included 24th-seeded Marcel Granollers on the men's side and 11th-seeded Marion Bartoli, No. 9 Li Na and No. 5 Petra Kvitova in the women's draw.

Andy Roddick, Serena Williams and Djokovic, the defending champion, were scheduled to play Tuesday.