The season's final Grand Slam US OPEN get underway this evening. Defending champion Novak Djokovic and fellow two-time winner Rafael Nadal come into play with injury concerns.World number one Djokovic, the 2011 and 2015 champion, admits he is "not 100 percent" after suffering a wrist injury on the eve of the Olympic Games where he was a shock first-round loser.Nadal, meanwhile, is also battling the effects of a left wrist problem which forced a mid-tournament withdrawal from the French Open and sidelined him until the Olympics where he was a gold medal winner in the men's doubles.The injury concerns, combined with the absence for the first time since 1999 of five-time winner Roger Federer, have put 2012 champion Andy Murray in the position of favourite. Play on the cavernous Ashe stadium starts with 2015 women's runner-up Roberta Vinci, the Italian seventh seed, facing Germany's Anna-Lena Friedsam.Vinci stunned Serena Williams in the semi-finals in 2015 before losing the championship match to Italian compatriot Flavia Pennetta who retired in the immediate aftermath of her first and only Grand Slam win.World number two Angelique Kerber, the Australian Open champion who can dethrone six-time US Open winner Williams as world number one in New York, opens against Polona Hercog of Slovenia. Action on Louis Armstrong Stadium starts with 2014 champion Marin Cilic against Rogerio Dutra Silva of Brazil. That's followed by former major winners Francesca Schiavone and Svetlana Kuznetsova.French Open champion Garbine Muguruza, the Spanish third seed, faces Belgian qualifier Elise Mertens.