Rafael Nadal was given a tough US Open workout as he started his campaign for a first title in New York with a confidence-building 7-6 (7/4), 7-6 (7/4), 6-3 win over Russian Teymuraz Gabashvili.

The Spanish top seed on Tuesday ran out a comfortable enough winner in the end, but he was made to work hard by an opponent who went for his shots at every opportunity, especially in a closely contested first two sets.

Nadal had the advantage of playing under lights in the night session at the Arthur Ashe Centre Court, avoiding the stifling heat of the day that had players gasping and reaching for ice packs at the changeovers.

The heat almost accounted for third seed Novak Djokovic, who needed to claw his way back from two sets to one and a break down before finally seeing off fellow Serb Viktor Troicki 6-3, 3-6, 2-6, 7-5, 6-3 in three hours and 40 minutes of punishing tennis.

Among seeded players to fall were 16th seed Marcos Baghdatis, who went down 6-3, 2-6, 1-6, 6-4, 7-5 to French veteran Arnaud Clement, and 24th seed Ernests Gulbis, who fell 6-2, 7-6 (7/1), 6-4 to Jeremy Chardy of France.

American 19th seed Mardy Fish almost joined them before he got the better of Jan Hajek of the Czech Republic 6-0, 3-6, 4-6, 6-0, 6-1 in a roller-coaster of a match. Spanish powerhouse Fernando Verdasco was also taken to the limit before he ended the upset hopes of Italy's Fabio Fognini 1-6, 7-5, 6-1, 4-6, 6-3.

Nadal had to wait until the seventh game of the third set before he finally managed to break Gabashvili's serve, having needed two 7-4 tie-breaks to take the opening two sets.

He then ran off the next two games to set up a second-round tie with Denis Istomin of Uzbekistan. "No one match is easy and especially in the big tournaments," he said. "The pressure is there against players who do not have much to lose and who play crazy, but I thought I played well.

"I served well. Concentration was good. The forehand is working well. The backhand is improving a lot and it just remains to have a bit more confidence, but that's the only thing. The basic things are really in the right way.

"I hit some terrible shots on the break points, but I played well in the tie-breaks and that's important for the confidence." Nadal is bidding in New York to become the seventh player in history to complete the career Grand Slam of Australian, French, Wimbledon and US Open titles.

If he does so, he would become, at 24, the youngest man in the history of the sport to achieve that fabled feat and the first to do so in New York since Rod Laver in 1962.

It would also make him just the fourth man in the Open era after Roger Federer, Pete Sampras and Rod Laver to win three consecutive Grand Slam titles following his back-to-back wins at the French Open and Wimbledon.

But in seven previous US Open campaigns, his best here has been semi-final appearances in the last two years, and Nadal agrees that the surfaces and balls used at Flushing Meadows are the least suited to his game of the four Grand Slam tournaments.

Djokovic's reward for the grit and courage he displayed against Troicki is a match against Philipp Petzschner of Germany for a place in the third round.

But the struggle once again exposed his vulnerability when playing in hot conditions with the temperatures at Flushing Meadows soaring to a peak of 35.5 degrees Celsius in mid-afternoon.

"Give credit to Viktor. He was playing well and serving incredibly well," he said. "Even if I would lose today it would have been deserved on his side. A couple of points changed the match and I was just fortunate to get through."

Baghdatis, one of the form players coming into New York, refused to blame the heat for his loss to Clement, instead saying that his batteries had already been at low going into the tournament.

"I was really heavy on court and not feeling very fit, very defensive and I didn't play very good tennis," he said. "Maybe a bit tired. It's been a month and three weeks I've been out here (United States) and that's a lot of time. And it's also first round of a Grand Slam and the nerves are there also.

Clement, who advanced to a second round tie with Eduardo Schwank of Argentina, said that he had initially struggled with the conditions which left him with "burning legs."

"So I tried to be very aggressive and to have short points. Was maybe the best tennis at the end for me. So it was a very good feeling." Compatriot Chardy said that an improved backhand had helped him see off Gulbis.

"Also I have put a lot of work in on improving my defense and it now gives me as much pleasure to win a point by defending as hitting a forehand winner."