There is only one question lingering before the start of the 2009 US Open on August 31 at the USTA Billie Jean King National Tennis Center at Flushing Meadows, New York City: Who can stop Roger Federer?

Roger Federer will seek his sixth straight US Open and 16th career Grand Slam singles title. With Federer’s last win in Wimbledon, he became the career leader in Grand Slam singles titles by surpassing tennis legend Pete Sampras. Federer has won five consecutive US Open titles but has not faced Rafael Nadal in any one of them. Nadal has yet to reach the US Open finals.

Federer beat Lleyton Hewitt in 2004, Andre Agassi in 2005, Andy Roddick in 2006, Novak Djokovic in 2007 and Andy Murray in 2008. Simply an incredible feat for a professional athlete. Every time Federer reaches the US Open finals, it is 100% guaranteed that he is going to walk away the winner.

After his win at Wimbledon, Federer also has the momentum coming into the US Open. He will be a huge favorite come tournament time.

Rafael Nadal has the best chance of beating Roger Federer. But Nadal has been experiencing knee problems. His injuries forced him out of Wimbledon and he was unable to reach the finals during the French Open. Expect Nadal to be rusty if he chooses to play in the US Open. A rusty Nadal is no match for a streaking Federer. Even when Nadal was healthy he needed to be in top form to beat Federer.

Americans Andy Roddick and James Blake will have the crowd cheering for them. The home crowd will pump them up during games but moral support is not enough to beat Roger Federer. Plus, Federer holds a mental advantage over Roddick after Federer’s victory over him in the Wimbledon finals.

Novak Djokovic is the wild card. When Djokovic is focused, he plays like the best tennis player on the planet. But Djokovic is too emotional and lets adrenaline get the best of him at times. He needs to learn how to calm down during games and concentrate on just playing tennis instead of letting the crowd affect his game.

There is no clear cut contender to Roger Federer’s reign at the US Open. Nadal, Roddick, Murray and Djokovic all have a chance to beat Federer. But Federer’s intangibles and court generalship make him the best tennis player on the planet.

If Nadal can miraculously heal his knee to full strength and sharpen his rusty tennis skills in time then maybe he can end Federer’s dominance at the US Open.