06/01/2012 01:03 EDT | Updated 07/31/2012 05:12 EDT

With a birthday during the French Open, Nadal celebrates at Roland Garros one way or another

PARIS - Rafael Nadal has made a habit out of celebrating at Roland Garros, and it's not just because his June 3 birthday falls during the French Open.

This year, his focus is so squarely on winning a record seventh French Open, he couldn't even remember exactly when he will turn 26.

"When is my birthday?" Nadal said Thursday after being asked if he had anything special planned. "I don't know the day."

When you play on clay like Nadal, the only date to remember is the day of the French Open final, and that's exactly a week later this year.

"Difficult to celebrate ... when you are in the middle of the tournament, but sure, I'm going to go for dinner with the team," Nadal said. "I don't know if some family going to come. I don't know yet."

The second-seeded Nadal improved his French Open record to 47-1 on Thursday, beating Denis Istomin of Uzbekistan 6-2, 6-2, 6-0. If he wins five more matches, he will break the record of six French Open titles he shares with Bjorn Borg.

Nadal wasn't the only record-breaker on court Thursday. John Isner, the American who won the longest match in tennis history two years ago at Wimbledon, lost 18-16 in the fifth set in another marathon match.

Also, Andy Murray overcame back spasms to reach the third round, while fourth-seeded Petra Kvitova advanced in straight sets.

On Friday, top-ranked Novak Djokovic and 2009 champion Roger Federer will play their third-round matches, while second-seeded Maria Sharapova will play in the second round.

Nadal has been masterful on the red clay of Roland Garros since his debut in 2005. His only loss came in 2009, when Robin Soderling beat him in the fourth round.

On Thursday, he was so good against Istomin that he even lamented allowing his opponent to have two measly break points.

Nadal saved them both.

"First set, I think, was good level," Nadal said. "Second one was good at the end, but in the middle of the set I had some problems with my serve, two break points in two games."

Murray had quite a different match. Playing first on Court Philippe Chatrier and barely able to walk because of his hurting back, he still managed to beat Jarkko Nieminen of Finland 1-6, 6-4, 6-1, 6-2.

The fourth-seeded Briton twice called for treatment on his back during the first set, and then again after losing the set. But then things started to change.

"I was a few points probably from stopping," Murray said. "I just didn't really want to stop the match. Then at the end of the second set I started standing up at the change of ends, and my back started to loosen up a little bit."

Despite being broken to open the second set, Murray started to move better. By the time he broke back for 4-4, Murray was the one getting stronger.

"I really never got the momentum back," Nieminen said.

Murray, who injured his right ankle at the French Open last year, skipped the Madrid Open with a back problem and said it was still affecting him after a three-set loss to Richard Gasquet in the third round of the Italian Open.

Isner was last on court in the main stadium, and eventually lost to Paul-Henri Mathieu of France 6-7 (2), 6-4, 6-4, 3-6, 18-16.

Two years ago, Isner beat Nicolas Mahut 70-68 in the fifth set at Wimbledon.

Thursday's long encounter forced Sharapova's match to be postponed because it lasted 5 hours, 41 minutes — the second-longest by time in French Open history. The record is 6:33.

The last set alone took 2:28.

"I served well," Isner said. "Just didn't do anything else that well."