A year ago, Kim Clijsters was the mom hogging the spotlight at the US Open. This time it is Mother Nature.

Unrelenting heat and swirling winds has transformed the last grand slam of the year into a battle against the elements and now Hurricane Earl is approaching New York, threatening to dump on the city that never sleeps.

It is little wonder then that the top players were in such a rush to get off the courts as quickly as possible on Thursday, battering their lower-ranked opponents as swiftly and ruthlessly as the wacky weather at Flushing Meadows.

For the second time this week, Roger Federer cruised to victory in straight sets inside Arthur Ashe Stadium. His 6-3, 6-4, 6-3 victim was Germany's Andreas Beck.

It was all over in one hour 41 minutes and even the Swiss master himself was impressed.

"It's the perfect start," he said. "I played Monday, had two days off. I had another easy one physically today, and here I am in the third round feeling like I'm completely in the tournament."

For Federer, it was all just business as usual. He did not repeat the magical between-the-legs trick shot he played in his opening match but still went through most of his repertoire as he prepares for the tougher matches that lie ahead.

If he maintains his early form throughout the fortnight, a 17th grand slam title could be his.

"Tougher matches will only be coming up now, I guess," Federer said. "It's gonna be interesting to see how the Saturday conditions are going to be with the hurricane sort of moving in. We'll see how that goes."    

Russia's Maria Sharapova was also in a hurry, trampling Iveta Benesova of the Czech Republic 6-1 6-2, but neither of the former champions could keep pace with Denmark's Caroline Wozniacki, the runner-up to Clijsters 12 months ago.

Russia's Vera Zvonareva, a finalist at Wimbledon this year, and Belgium's Yanina Wickmayer, semi-finalist at the US Open last season, also raced to straight-sets wins on another steamy day when the Extreme Weather Policy was invoked as temperatures climbed past 91 degrees Fahrenheit (33 Celsius).

Serbia's Jelena Jankovic, the fourth seed, survived after being pushed to a third set in her win over Mirjana Lucic.

Russian sixth seed Nikolay Davydenko spent little time on the sun-baked court but only because he was hammered 6-3, 6-4, 6-2 by Frenchman Richard Gasquet. He had been troubled by injury but said his real problems may be in his mind.

"I don't know if it's my wrist or my head," he said. "I don't know if I need to have a coach, a mental coach or if I need to go somewhere to change my brain.

The casualty rate among the seeds in the first four days of the championship has been almost as brutal as the baking heat with 20 making early exits, including four more Thursday.

Aravane Rezai and Maria Jose Martinez Sanchez were knocked out of the women's draw while Croatia's Marin Cilic, the men's 11th seed, was upset by Japan's Kei Nishikori 5-7, 7-6, 3-6, 7-6, 6-1 in one of the few matches that went the distance.

Sweden's two-time French Open finalist Robin Soderling is looming in the quarter-finals for Federer after he outgunned one of the biggest servers in men's tennis, beating American Taylor Dent 6-2, 6-2, 6-4.

Novak Djokovic capped a perfect day for the favourites on centre court at the US Open on Thursday by beating Germany's Philipp Petzschner to reach the third round in the year's last grand slam.

Third-seeded Djokovic closed out the irresistible display by the seeds with a 7-5, 6-3, 7-6 victory under the lights at Arthur Ashe Stadium that marked the fifth successive straight-sets win for the seeds on centre court.

The Serb had to work harder than his predecessors at Arthur Ashe as Petzschner put up a spirited fight in an entertaining tilt that was decided by 8-6 in the third-set tiebreaker.

Djokovic, Open runner-up to Roger Federer in 2007 and semi-final loser against the Swiss master the last two years, will go up against unseeded American James Blake, who advanced against Canadian Peter Polansky.

Wozniacki is looming as the favorite to win her first grand slam title after a flawless start to the tournament.

Wozniacki needed just 47 minutes to breeze past Chang Kai-chen of Taiwan 6-0, 6-0 and will face Sharapova in the fourth round if they both win their next matches.

Promoted to top seed after world number one Serena Williams withdrew with a foot injury, Wozniacki won three lead-up tournaments and has carried her form into the US Open.

"When you're winning, you have that confidence," she said. "You go out on the court and you know what to do. You're in your own bubble. That's what I'm aiming for."