Five-time US Open champion Roger Federer believes lots of sleep has played an important part in his good form of late, as he prepares for his semi-final at Flushing Meadows against Stan Wawrinka.
The 34-year-old, 17-time grand slam-winner believes napping, coupled with gym work and on-court practice, is the best way to prepare for his 10th semi-final in New York City and his 20th match against his Swiss compatriot and long-time friend.
Federer admitted that he will try and get about 10 hours of sleep before Friday's semi-final against the French Open winner.
"Sleeping has become quite important," Federer said after beating French 12th seed Richard Gasquet in Wednesday's quarter-final.
"I make sure I sleep enough, as well. Like when I went to bed after the John Isner match (in the round of 16) it got quite late and I couldn't sleep quite as much as I wanted to.
"Because I believe it's really the sleep that gives you energy again down the road. That's why the next two days are very important for me in terms of sleeping."
Federer has been in sublime form during the US hard-court swing and won the US Open tune-up in Cincinnati without losing his serve, a triumph which included straight sets wins over Andy Murray and Novak Djokovic.
Wednesday's quarter-final against Gasquet was another illustration of how well Federer is playing at the moment – he hit 50 winners, fired 16 aces and faced just one break point in the 6-3, 6-3, 6-1 win.
Federer has a 16-3 career record against Wawrinka and while the 30-year-old won their last encounter – a quarter-final at the French Open – he has yet to triumph against his illustrious rival on a surface other than red clay.
"I think a lot comes through practice for Stan, because he's worked very hard throughout his career," Federer continued.
"It took him a while to figure out exactly what his possibilities were. I don't think he was a guy who always had enough confidence. I always thought he was a better player than he actually was, but somehow something was holding him back maybe.
"I think only once when he really started to break through and he had some big wins."
Following his victory at Roland Garros, Wawrinka believes he is finally able to compete with Federer on an even keel for the first time in his career.
"I think now we are both nervous when we enter the court. Before it was only me. I was nervous because I knew I wasn't at his level," Wawrinka.
"Now I think we can see that he was also nervous every time we play each other the past few years. That's a big difference."
Wawrinka will be playing in his second semi-final at Flushing Meadows, having previously reached the last four there in 2013.