NEW YORK (AFP) - Forgive Australian Open champion Novak Djokovic if this US Open is one Grand Slam event he would like to forget. The third-seeded Serbian lost 6-3, 5-7, 7-5, 6-2 to Swiss second seed Roger Federer in a Saturday semi-final rematch of his straight-set loss in last year's US Open final. He was unhappy about having to make an early start to the match because of an oncoming tropical storm bringing rain showers and already stressed out about innuendoes he fakes injuries for medical timeouts to disrupt opponents. "It has been a very exhausting tournament for me mentally and physically. That's one of the main issues," Djokovic said. "I knew I had to be 100 percent fit to win against a player who has won four times here. If you're not able to hold on you're not able to win." Djokovic finished off a late-night quarter-final against Andy Roddick early Friday and was back on court in Arthur Ashe Stadium 34 hours later. "The schedule was not the best for me," Djokovic said. "If you finish a couple matches at 1 in the morning and you go to sleep at 4 in the morning and then two days afterward you have to play at 11, it's not really the best thing you could want to have. But what could I do?" Djokovic was heckled by the crowd against Federer after being booed after his victory over Roddick for ripping into the American over comments about how the Serbian had "16 injuries". Each man later apologized but most fans were clearly against Djokovic. "I've said what I needed to say," Djokovic said. "I'm not looking at the things that has passed already. I'm just looking at the future. "I want to forget some things as soon as possible. I will always remember this tournament in the best possible way. I don't want to take the bad memories out of it, just turn the page and try to do better next year." Djokovic can look toward defending his title at Melbourne and said he is looking forward to improving his passt efforts in the season-ending ATP event in Shanghai, where he has not won. And he simply wants to improve his game. "I can be an even better player," Djokovic said. "I still need to improve some things in my game but there is still a lot of time. I will try to be more aggressive, get more to the net and use opportunities that are given to me."