The Scot, who reached the final last year, dropped his first set of the tournament in his second-round win over Paul Capdeville of Chile in steamy 90F heat at Flushing Meadows.
World No 2 Murray plays huge-serving American Taylor Dent in the third round today and with Juan Martin Del Potro and Rafael Nadal in his section of the draw, he knows he has to hit top form.
"I'm going to have to play better than I did in the first two rounds if I want to win," Murray said.
"But I feel like I can get better. This is my favourite surface.
"I think I can win it and I'd be disappointed if I didn't, but I know that you can still have a good Grand Slam without winning it."
The US Open is the only one of the four Grand Slams to play the semi-finals and final on successive days, next Saturday and Sunday, but Murray hopes his extra fitness work will see him through.
He added: "It's basically five matches in eight days. It's worse for the guys who played their first match last Wednesday because in theory they're playing seven matches in 12 days and guys who play on Monday are playing seven matches in 14.
"I would sign up for the seven in 14 days. It's a little bit tough on some of the players but hopefully everyone is fit enough to deal with it."
On court last night tournament favourite Roger Federer overcame a fierce battle from old rival Lleyton Hewitt.
The world No 1, chasing his sixth straight title here and his 16th grand slam title in all, trailed Aussie Hewitt by a set before pulling through with a 4-6, 6-3, 7-5, 6-4 win.
A lacklustre Novak Djokovic also survived a scare against American world number 276 Jesse Witten before clinching a 6-7 6-3 7-6 6-4 victory.
In a match containing 15 breaks of serve, the Serbian fourth seed was below his best and Witten pushed him hard before finally wilting after three hours, 28 minutes.
Please note: All comments are moderated.
Tick this box to accept our
TERMS & CONDITIONS
This article has 0 comments