World ranking: 1 Career singles titles: 27 ; Grand Slam singles titles: 3 Best US Open result: Runner-up (2007, 2010)
2011 has seen Djokovic put together a 57-2 winning record, capture nine titles - including the Australian Open and Wimbledon -- as well as securing the world number one spot. But a shoulder injury which forced him to quit the Cincinnati Masters final against Andy Murray last weekend has put a question mark over his staying power at the US Open.
World ranking: 2 Career singles titles: 46 ; Grand Slam singles titles: 10 Best US Open result: Champion (2010)
Defending champion, when he completed the Career Grand Slam, Nadal has endured a tough summer since winning a sixth French Open title. Brushed aside by Djokovic in the Wimbledon final, he also lost his world number one ranking to the Serb. A second round loss in Montreal followed by a quarter-final exit in Cincinnati showed that Nadal's foot injury is still a problem while burning his right hand on a restaurant hot plate did little to improve his mood.
World ranking: 3 Career singles titles: 67 ; Grand Slam singles titles: 16 Best US Open result: Champion (2004, 2005, 2006, 2007, 2008)
Having celebrated his 30th birthday, and with the last of his record Grand Slam titles coming in Australia in 2010, Federer is desperate to prove that he is still a contender. Defied critics in reaching the French Open final by ending Djokovic's 41-winning start to the season. But then surrendered a two-sets to love lead to lose to Jo-Wilfried Tsonga in the Wimbledon quarter-finals before third round and last eight departures in Montreal and Cincinnati.
World ranking: 4 Career singles titles: 18 ; Grand Slam singles titles: 0 Best US Open result: Runner-up (2008)
Under pressure to end his country's 75-year wait for a Grand Slam men's singles champion. But with injury clouds over Djokovic and Nadal as well as a fear that Federer's best days are behind him, Murray could find himself in the box seat. Enjoys the boisterous nature of the US Open and arrives buoyed by victory over Djokovic in the Cincinnati Masters final.
World ranking: 18 Career singles titles: 9 ; Grand Slam singles titles: 1 (US Open 2009) Best US Open result: Champion (2009)
The giant Argentine remains an outside bet for a title repeat but also the man nobody wants to face. A former world number four, he captured the 2009 title by becoming the first player to beat Nadal and Federer in a Grand Slam tournament. Career went into a tailspin in 2010 when he missed eight months with a wrist injury.
World ranking: 8 Career singles titles: 6 ; Grand Slam singles titles: 0 Best US Open result: Quarter-finalist (2008)
Fish has supplanted the fast-sinking Andy Roddick as the US number one. Has enjoyed an impressive summer on American hard courts, winning in Atlanta, followed by runners-up spots in Los Angeles and Montreal and a semi-final at Cincinnati. Emotional favourite to reach men's final which will be staged on the 10th anniversary of 9/11.
A lot has changed since the 2010 US Open where Rafael Nadal defeated Novak Djokovic for his maiden Grand Slam title in New York. Rafa is no longer the unstoppable force, nor the World No.1 or even the favourite. All these honours have been passed on to Djokovic. Currently, all three top players, which includes Roger Federer, are battling fitness or form worries. But, that doesn't change the usual scenario of them being the top contenders for the tournament.
A look at the men likely to be in contention for the US Open title, the final Grand Slam tournament of the season: