NEW YORK – Andy Roddick stunned the tennis world by announcing that the U.S Open would be his last tournament on Thursday but there was no sign of the end of the road for his contemporaries Roger Federer and Serena Williams on day four at Flushing Meadows.Federer led the tributes for Roddick after defeating Bjorn Phau with an evening exhibition to reach the third round of the men’s draw, while Serena added her own plaudits after remaining on course for a fourth U.S. Open crown with a victory over Maria Jose Martinez Sanchez.Roddick’s announcement of his impending retirement came shortly after France’s fifth seed Jo-Wilfried Tsonga produced his worst match of the year to be the first big-name casualty of the men’s draw.The former world number one and U.S Open champion said he realised during his first-round victory over Rhyne Williams that he had lost the desire to remain on tour."I just feel like it’s time,” Roddick, who celebrated his 30th birthday on Thursday, said. "I’ve always wanted to, in a perfect world, finish at this event. I have a lot of family and friends here."I thought all year I would know when I got to this tournament. When I was playing my first round, I knew. Playing here, I don’t know what it was. "I couldn’t imagine myself being there another year.”  Roddick was due to play Australian Bernard Tomic on Arthur Ashe Stadium on Friday night in what is now sure to be a highly-charged atmosphere. Roddick won the 2003 U.S. Open and was a Wimbledon finalist in 2004, 2005 and 2009.Top seed Federer absolutely dominated German Phau to win 6-2 6-3 6-2 in the opening match of Thursday’s night session before paying tribute to Roddick, who he defeated in three Wimbledon finals.In the women’s draw, Serena, though not at her best, was an easy 6-2 6-4 winner over Martinez Sanchez but second-seeded Angieszka Radwanska struggled before peeling off 11 straight games in a 4-6 6-3 6-0 defeat of Carla Suarez Navarro.While Serena advanced, her sister Venus lost 6-2 5-7 7-5 to Germany’s sixth seed Angelique Kerber in a tense battle under the lights following Federer’s dominant triumph.Venus, twice a champion at Flushing Meadows, blasted 43 winners but committed un uncharacteristic 60 errors in the two-hour, 45-minute loss to the southpaw Kerber, a semi-finalist here a year ago.Teenager Sloane Stephens again lived up to the hype with a 5-7 6-4 6-2 win over Tatjana Malek and there was more American success when 32-year-old men’s wildcard James Blake wound back the clock to beat 24th seed Marcel Granollers 6-1 6-4 6-2.