New York (AFP) - Five-time champion Serena Williams reached her first Grand Slam quarter-final of the year at the US Open on Monday, setting up a clash with Flavia Pennetta in a duel between the two oldest women left in the draw.World number one Williams, the two-time defending champion, eased past world number 50 Kaia Kanepi, 6-3, 6-3, for a fourth win over the Estonian."It's my first quarter-final of the year at the majors -- at last I did it," said the 32-year-old American, who had fallen in the fourth round in Australia, the third round at Wimbledon and suffered a second round French Open exit."It was a tough match today.