Roger Federer was twice made to come from behind for his 55th consecutive win on North American hardcourts when overcoming Thailand's Paradorn Srichaphan 7-5, 6-4 in the Cincinnati Masters on Tuesday.
The Swiss world number one maintained the torrid pace which lifted him to his seventh trophy of the season at the weekend when he beat Richard Gasquet in Toronto.
Gasquet could not maintain his form, however, and went down in the first-round 7-5, 7-5 to Spaniard Tommy Robredo.
Federer handed Srichaphan a 15th first-round defeat this season after trailing a break in both sets, but the Swiss was able to storm back to earn a third victory over Asia's top player.
"It was an extra tough match, he was playing well from the start," Federer told reporters. "But I got into the match and was able to win it."
Second seed Rafael Nadal overcame 10 aces from American Sam Querrey before defeating the teenager 6-7, 6-2, 6-3.
Querrey is ranked 178th in the world and Nadal, who prevailed in just over two hours as he broke three times while never losing serve, paid tribute to him.
"He has an unbelievable serve but in the third set I improved my game a lot," Nadal told reporters. "My forehand got better and I relaxed."
The Spaniard, who won the last of his five 2006 titles at Roland Garros in June, was beaten last week in the Toronto third round by Tomas Berdych.
"I need to get some more confidence in my game," he said. "My movement also needs to improve and I need to play with more aggression."
Fourth seed Ivan Ljubicic dismissed Greg Rusedski 6-3, 6-4 as the Briton lost his sixth consecutive first-round match.
Andy Murray defeated Tim Henman in the second battle of Britain in as many weeks, earning a 4-6, 6-4, 7-5 victory to book a place in round two against Federer.
The Scottish teenager had beaten his 31-year-old mentor in Basel last year and again last week in the Toronto second round.
Last year's finalist Andy Roddick made a return after tearing a rib tendon last month, posting a 6-7, 7-6, 7-6 opening win against Italy's Daniele Bracciali.
After being unable to bend over to tie his shoes three weeks ago, Roddick was not bothered by a lingering bit of pain. He took a precautionary medical timeout in the second set.
"I was just a little worried. It got a little bit worse as the match went on," Roddick told reporters. "I just wanted to make sure that was normal and that I wasn't risking anything."
