Federer, Serena untroubled at stricken US Open

Roger Federer of Switzerland returns a shot against Dudi Sela of Israel during Day Four of the 2011 US Open, at the USTA Billie Jean King National Tennis Center in New York City.

Five-time US Open champion Federer eased past Israel's world number 93 Dudi Sela 6-3, 6-2, 6-2 for his 225th win at a major, one more than Andre Agassi and just eight behind Jimmy Connors's all-time mark of 233.

The third seed next faces Croatian 27th seed Marin Cilic who put out 18-year-old Australian Bernard Tomic, the youngest player in the draw, for the loss of just three games.

"Not much trouble on my serve, and from the baseline I also thought I had the upper hand. When it's like that, obviously it's tough for the opponent, but I just think I was superior today," said Federer.

"It was a good match for me in breezy conditions It was a bit tricky early on to find the rhythm. That's why I was happy to get the first break in the first set."

Federer unleashed 31 winners to Sela's 10 in his 77-minute victory, allowing his opponent just eight points on serve.

Triple women's champion Serena Williams took only 49 minutes to dispose of Dutch qualifier Michaella Krajicek 6-0, 6-1 and could face Belarusian Victoria Azarenka for a last 16 place if the fourth seed beats Argentina's Gisela Dulko.

Williams, seeded 28 after spending most of the last year fighting injury as well as life-threatening blood clots on her lungs, has dropped just three games in her first two rounds.

She saw off Krajicek, the 2006 junior champion, with a 10th ace, having unleashed 25 winners to the hapless Dutch girl's five.

The American insisted that she had not been distracted by seeing sister Venus withdraw from the tournament 24 hours earlier after being diagnosed with an auto-immune disorder.

"It really wasn't that difficult, to be honest. She wants me to do the best; she wouldn't want me to suffer. So now, if anything, it should motivate me more," said Williams.

Meanwhile, the number of walkovers and injury-enforced retirements at the tournament climbed to 13.

Czech 23rd seed Radek Stepanek called it quits in the third set against Juan Monaco of Argentina with a shoulder injury.

Former French Open champion Ana Ivanovic reached the third round without hitting a ball when Czech player Petra Cetkovska, who beat the Serb at Wimbledon and was runner-up at New Haven at the weekend, withdrew through injury.

Former world number one Juan Carlos Ferrero, the 2003 runner-up, was also keeping the tournament medical staff busy as he twice needed treatment on a blistered hand and foot before causing the biggest shock of the day.

The 31-year-old defeated French seventh seed Gael Monfils 7-6 (7/5), 5-7, 6-7 (5/7), 6-4, 6-4 to reach the third round where he will take on compatriot Marcel Granollers.

Serbian 11th seed Jelena Jankovic also needed on-court treatment on her back before wrapping up a 6-3, 6-4 win over Australia's Jelena Dokic.

Also going through were Italian seventh seed Francesca Schiavone, who beat Croatia's Mirjana Lucic, and German 10th seed Andrea Petkovic who came from a set and 3-0 down to beat China's Zheng Jie 3-6, 6-3, 6-3.

Russia's 2004 champion Svetlana Kuznetsova was untroubled against Britain's Elena Baltacha, winning 6-4, 6-3.

In the men's event, there were wins for Czech ninth seed Tomas Berdych, Serb number 20 Janko Tipsarevic as well as Germany's Tommy Haas who, at 33, is the oldest player left in the men's draw.

Haas, whose ranking has tumbled to 475, is playing in his 14th US Open and he made the third round with a straight sets win over Colombia's Alejandro Falla.

Later Thursday, world number one and top seed Novak Djokovic tackles Argentina's Carlos Berlocq as he looks for victory number 59 in 61 matches in 2011.

US eighth seed Mardy Fish takes on qualifier Malek Jaziri, the first Tunisian man to play in a Grand Slam main draw.

Women's top seed Caroline Wozniacki takes on Dutchwoman Arantxa Rus.