Defending champions Roger Federer and Serena Williams are both through to the third round of the US Open. Federer won his second-round match against Germany's Simon Greul 6-3 7-5 7-5 to set up a clash with 2001 champion Lleyton Hewitt. Williams continued her blistering progress in the competition with a quickfire victory over Melinda Czink, beating the Hungarian 6-1 6-1. Her sister Venus has also booked her place in the last 16 of the competition at Flushing Meadows beating Bethanie Mattek-Sands 6-4 6-2. Meanwhile, the men's third seed Rafael Nadal eased past France's Richard Gasquet in straight sets, showing no signs of the knee problems which have plagued him recently as he set up a third-round encounter with Nicolas Kiefer of Germany. Elsewhere, former champion Marat Safin bid farewell to major tournaments with a 1-6 6-4 6-3 6-4 defeat by Austrian Juergen Melzer. "It's the end and the last one," Safin said. "Could have been a better ending but still okay. No regrets. I don't care about losses anymore." The 29-year-old Russian, who won the 2000 US Open and was once the world's top-ranked player, has already announced plans to retire at the end of the year.