Andy Murray was grateful for an evening free of drama as he cruised past Feliciano Lopez early today to reach the fourth round of the US Open under the lights on Arthur Ashe Stadium.

The world No.4 hared out of the traps, winning the first 14 points and not dropping a point on his serve in a one- sided first set.

The second was much tighter, with Lopez, against whom Murray had dropped only one set in five previous matches, finding some form.

But an untimely seventh double fault gave his opponent the crucial break in the ninth game and he eased to a 6-1, 6-4, 6-2 victory.

Murray was delighted to avoid a repeat of his previous five-setter against Dutchman Robin Haase.

He said: "It was better. They were very tough conditions at the start as well. It was pretty windy. I had to get the feet going early.

"When you can get an early break it can kind of set the tone for the rest of the match. Tonight that was the case.

"And it was important because obviously, after having a long match the other day, especially playing late at night, if you don't have to play a three or four-hour match (it's much better) because it's not that easy to recover."

Murray's next opponent will be 22-year-old American wild- card Donald Young, whom he faces tomorrow. In the second round he knocked out Stanislas Wawrinka, Murray's conqueror last year, and yesterday he was a straight-sets winner over 24th seed Juan Ignacio Chela.

Young beat Murray in Indian Wells in March during the 24-year-old's post-Australian Open malaise, and he knows it is a match he must be ready for after an up-and-down first week in New York.

He added: "So much can change in a couple of days.

"You just need to make sure you stay focused on the next match. It's a big match for me because obviously of what happened earlier in the year.

"But, energy-wise, I'll be feeling good going into that one hoping for a long second week."

Rafael Nadal will return to Flushing Meadows for his fourth-round clash with Gilles Muller tomorrow hoping to make the headlines for what happens on the court rather than off it.

The defending champion was impressive in beating David Nalbandian 7-6 (7-5), 6-1, 7-5, playing by far his best match on hard courts this summer. But the Spaniard's post-match press conference came to an abrupt halt when he began grimacing and clutched his right thigh.

The 25-year-old was suffering from cramp in his quad muscle and hamstring and slid off his chair while the physio was hastily sent for.

Nadal received treatment for a good 10 minutes lying on the floor behind the desk in the main interview room before getting to his feet somewhat gingerly.

Nadal will return to the practice courts today, but 2009 champion Juan Martin Del Potro is on his way home, beaten by Gilles Simon yesterday in his first defeat at Flushing Meadows for three years following the wrist injury that ruled him out last season.

Today's men's schedule has Novak Djokovic take on Ukrainian Alexandr Dolgopolov, Jo-Wilfried Tsonga faces Mardy Fish and Roger Federer up against Juan Monaco of Argentina.

Grand test for Serena and Caroline

American Serena Williams and Caroline Wozniacki face former Grand Slam title winners at the US Open later today as the last major of the year enters the second week.

Williams will play Serbia's Ana Ivanovic, the 2008 French Open champion, while Wozniacki meets Russia's Svetlana Kuznetsova, who has won both the US and French Open singles titles.

Williams and Wozniacki are overwhelming favourites to win their fourth-round matches and eventually clash in the semi-finals, but neither player is taking anything for granted.

"She's playing well," Williams said of Ivanovic. "She's incredibly fit right now."

The big-hitting American has battled back to the top of her game after a blood clot left her on her "death bed" earlier this year.

She said: "I love tennis, I love the battle, but health puts everything in perspective.

"I realise now that life is so precious and things could be a lot worse. But I've worked hard on my game to get this far and I'm enjoying it."

Wozniacki, the current world No.1, said she was expecting a tough battle against Kuznetsova.

"I haven't thought about how I'd play her," said the Dane.

"She's a tough competitor. She can play very aggressive. It's a match that definitely would need me to play on my best."