( CNN ) -- Crushing a string of opponents before dispatching Novak Djokovic in four sets in the U.S. Open final , Rafael Nadal was back to his ruthless best , with not a hint of the injury problems which have threatened to blight his career , even during a year which has seen him claim two grand slams . But the Spaniard has admitted to CNN that he had real fears that as he made yet another comeback he would fall short of his own incredible standards . `` Sure I had doubts , everyone has doubts , '' said the 27-year-old Mallorcan . `` When you are injured you doubt if you going to be able to come back and play at 100 % . '' Closing fast on Djokovic 's No.1 spot , Nadal has spent two lengthy spells on the sidelines through knee injuries , both times making a strong comeback . Returning to the ATP Tour in February , Nadal clicked straight into gear , culminating in his eighth victory in the French Open . But come Wimbledon his battered body could take no further punishment and Nadal was a shadow of his normal self as he crashed out in the first round to unheralded Steve Darcis , clearly troubled by knee problems . The doubters were out in force again and with Nadal sidelined yet again , Djokovic and Wimbledon champion Andy Murray were predicted to share the grand slams between them in the foreseeable future . They were reckoning without Nadal 's incredible determination and joining the circuit again for the pre U.S. Open hard court series , the Mallorcan looked as if he had never been away , claiming titles in Montreal and Cincinnati before his Flushing Meadows triumph . The mixture of joy and relief were there for all to see as Nadal savored every moment on the Arthur Ashe Stadium Court in claiming his 13th career grand slam . `` When you are coming back after low moments victories are all the more special and more emotional , '' Nadal admitted . `` I enjoy it now because in a few years I wo n't have the chance to play like I did in the U.S. Open final . '' The manner of his victory suggested that Nadal could easily outstrip all-time grand slam record holder Roger Federer , who has 17 in his trophy room . But always at the back of Nadal 's mind is the possibility his knee tendon problem might flare up again so he is taking nothing for granted . `` We need our knees , without our knees it is impossible to play well , sometimes I still have pain , but the most important thing is that at the moment I am able to play without limitations , '' said the newly crowned U.S. Open champion . Nadal has been a force on the circuit for approaching a decade since bursting to prominence as a precocious teenager , particularly on his favorite clay surface . His all action game was an immediate crowd pleaser but he admits that he takes a more measured approach these days . `` When you are a kid you are able to play with a different style , crazy jumping and all that , '' added Nadal . `` That moment has passed but my love and passion for the game is still the same . '' All that spells bad news for those battling him at the elite end of the men 's game with plenty to play for still in 2013 , including the ATP World Tour Finals in London , just about the only title which has eluded him .
Rafael Nadal won 13th grand slam title at the U.S. Open . Closing on the all - time record of wins held by arch rival Roger Federer . Victory came after early exit at Wimbledon to Donald Johnson . Nadal has been troubled by knee tendon problems in recent years .