Rafael Nadal

Even for the fittest player in tennis, the rigours of months of tournaments — and a recent return from the Olympics — take a toll. On Monday, the first day of the US Open, the weariness showed in Rafael Nadal. In his first Grand Slam match as the world’s No. 1 player, Nadal needed three hours and two tie breakers to defeat the qualifier Bjorn Phau, 7-6 (7-4), 6-3, 7-6 (7-4).

“I think I helped a little bit, him to play to this level,” Nadal said. “He played well today, but I didn’t play with normal intensity. I played with a little bit less intensity than last few months for sure. Probably I’m a little bit tired more than usual.”

Nadal has always struggled on the hardcourts at Flushing Meadows, where he lost in the fourth round last year. This is the only major in which he has never made it to the semi-finals. But he has had an extraordinary season, winning the French Open, Wimbledon and an Olympic gold medal on the hardcourts in Beijing.

Despite flying from the United States to Beijing and back in the last two weeks, Nadal said jet lag was not as much a problem as mental fatigue from a gruelling season. He has won eight titles this year and has won 39 of his last 40 matches. The good news for Nadal is that the schedule makers will probably give him a break and not have him play his second-round match against Ryler de Heart until Thursday.

“I don’t want to say another time I’m tired,” Nadal said. “I am a little bit tired, yes, but it is the US Open, so I have to try my best here.”

Nadal rose to prominence on the slower clay courts at the French Open, in which he can use his supreme conditioning to outlast opponents. But as his game has become more well rounded, he has had success on the fast hardcourts this year. He has the most hardcourt victories on the ATP Tour this season, and has won hardcourt titles in two Masters Series events and at the Olympics.

This is the first time he has been the top seed at a Grand Slam, and anything less than another epic meeting with Roger Federer, who is trying for his fifth United States Open title in a row, will be a disappointment for fans. But for Nadal, that does not seemed to matter.

“I never talk about playing against Federer,” Nadal said, noting that he was focusing only on the next round. He added, “When I was No. 2, the goal was the same, to win the US Open, but the goal wasn’t win the US Open to be No. 1.”

That was a stark contrast to Phau, a German who had never made it past the second round at a major. As the 136th-ranked player in the world, he was expected to go quickly and quietly. But the first set took more than an hour, and the first break of serve came in the tie breaker, when Phau hit a forehand long. After Nadal won the set, he had a trainer treat a blister on his left foot.

The next service break did not come until the sixth game of the second set, when Nadal broke Phau to take a 4-2 lead. For a while, it seemed as if Nadal had finally taken control. But Phau ran down shot after shot, keeping Nadal on the court far longer than he anticipated. Nadal served for the match at 5-4 in the third set, but Phau broke him.

“I am tired, believe me,” Phau said. “I made miles today. For me, it’s a positive because I saw I can play with the No. 1 player in the world.”

Elena Dementieva, the fifth seed in the women’s draw, can surely appreciate Nadal’s troubles. After her first-round match, an unexpectedly difficult 6-4, 7-5 victory over Akgul Amanmuradova, Dementieva acknowledged that she had a bit of an Olympic hangover. She said she was still thinking about the gold medal she won in Beijing.

The women’s field is wide open, and Dementieva is among several players who could emerge as No. 1 in the women’s rankings.

But for Dementieva, it will be difficult to top her Olympic moment. She said she watched the closing ceremony Sunday and her mind was still in China, even though she had been in New York since Wednesday.