NEW YORK (AFP) Andy Roddicks second-round exit from the US Open has pushed a new set of rising American men into the Grand Slam spotlight, hoping to advance the legacy of such legends as Pete Sampras and Andre Agassi. Sam Querrey, Mardy Fish and John Isner - all clustered around 20th in the rankings - carry US hopes of making the next step toward tennis stardom during the Flushing Meadows fortnight. I think its a great thing we have four guys in the top 20 right now. Im happy to see those guys do well, Roddick said. I have felt like its my responsibility to try to do what I can as far as helping those guys out. Serbias Janko Tipsarevic beat ninth seed Roddick 3-6, 7-5, 6-3, 7-6 (7/4) and delivered a tough critique on the 2003 US Open champion, saying he needs to make some major changed if he hopes to win a second Grand Slam crown. Definitely he needs to change something to win a Grand Slam, Tipsarevic said. He needs to be more aggressive but I think he can (win a Slam). He needs to change his game style a little bit, going for a little bit more, especially from his forehand. Roddick, 28, made his earliest US Open exit since a 2005 first-match loss. People say that he was much more dangerous when he was young because he was really going for the forehand every chance that he had. Now I just dont see that, Tipsarevic said. Hes going to wait for the mistake of the opponent rather than go for a big shot. Hes a kind of player that you need to beat. Roddick, who has been fighting mononucleosis, called his form disappointing but also not the worst it has been and notes that I know when Im playing well Im able to get deep into tournaments. His stumble from the top 10 last month left no US man in the top 10 for the first time in the 37-year history of the rankings. I didnt really feel much of a responsibility to be the guy in the top 10, Roddick said. That should fall maybe on some of the guys that have never been in the top 10. Enter Querrey, 22, whose fourth-round Wimbledon run matched his 2008 US Open as best Slam showing. The 22nd-ranked playmakers wins this year at Memphis, Belgrade, Queens and Los Angeles leave him behind only Rafael Nadal in 2010. Chasing top-ranked Nadal and 16-time Slam champipn Roger Federer has come only after years of practice against them. The more I played Roger and Rafa and Andy and practiced with them, you take the occasional set off them in practice and a set or two in the match and you beat a top 10 guy, then you kind of start to get the belief that you could beat these guys too, Querrey said. It definitely takes a couple of years. Isner, ranked 20th, reached the fourth round of the US Open last year and the Australian Open this year for his best Slam run. Isner, 25, is trying to show his game is more than a big serve. Ive been in the top 20 now for more than two months so I know I belong, he said. What keeps me going is I dont want to fall behind. I want to keep climbing. The more matches, the more mature you get on tour, the better thats going to become. I think Sam and I are both realizing that now. I feel that both of us are going to keep climbing. Fish, 28, reached the 2008 US Open quarter-finals and the 2007 Australian last eight. He dropped 30 pounds this year and feels ready for a Slam semi-final breakthrough. I havent shown that I can beat the top players in three out of five sets, Fish said. On the other hand, I feel like a completely different player. How far that takes me, I have no idea. But Ive never been fitter and mentally as strong. Ive never wanted it more, and so hopefully that goes a long way. US veteran James Blake, 30, has stumbled from the top 10 to 108th in the rankings due to injuries. He welcomes the next generation. Its a great sign for American tennis to let people know that its not just Andy and myself, the guys that are getting older, Blake said.