Murray vows to improve as Nadal also through

(CNN) -- World number two Andy Murray vowed to make sure his preparations are right for his third-round match in the U.S .Open, after seeing off Chile's Paul Capdeville on Friday.

Playing in 80-degree heat at the Arthur Ashe Stadium, Murray beat his former training partner 6-2 3-6 6-0 6-2 in two hours and seven minutes.

However, he was disappointed with his performance in the second set of a match against a player ranked 87 in the world.

Murray was lackluster and admitted after the match he did not feel physically right during the second set.

He told Sky Sports: "I had three good sets and one bad one. I got off to a bad start in the second set, which gave him some confidence, but then I picked up and finished it off well.

"I had a bit of a down, physically. I didn't feel exhausted, just maybe (it was) that I didn't eat enough or too close to the match.

"I had the same problem a few years ago in 2005 against Andrei Pavel, when I ended up throwing up -- having not eaten enough and drunk too much," added the Briton.

Murray will now play the winner of the second-round tie between American wild card Taylor Dent and Spain's Ivan Navarro.

Meanwhile, third seed Rafael Nadal saw off Nicolas Kiefer of Germany with a 6-0 3-6 6-3 6-4 win late Friday, sixth seed Juan Martin Del Potro fired 13 aces to beat Austrian Jurgen Melzer 7-6 6-3 6-3 and French seventh seed Jo-Wilfried Tsonga hit 11 aces to defeat Jarkko Nieminen 7-5 6-3 6-4.

Spain's Juan Carlos Ferrero, the 2003 French Open champion and U.S. Open runner-up, fired 17 aces to beat German Philipp Petzschner 1-6 3-6 6-4 6-2 6-4.

Up next is French ninth seed Gilles Simon, who ousted Brazil's Thomaz Belluci 6-3 6-2 6-4 with Del Potro possibly awaiting the winner.