MONTREAL: Rafael Nadal spent just 36 minutes in his comeback from a two and a half month injury absence as David Ferrer retired hurt while trailing 4-3 in their second round match at the Montreal Masters.

The result was an anti-climax for world number two Nadal, who has been resting tendinitis-plagued knees ever since losing on May 31 at the French Open.

"I must be happy, because I didn't play terrible," said the second seed. "In the next round, I have another chance to continue to improve. Every match, every game is important to feel better for me.

"My knees felt OK, but I need more days to have real test."

Nadal, the defending champion, drew massive applause as he went onto the court with his fellow Spaniard and showed few outward signs of rust after his long absence.

"It's tough to have to go out and have to leave the court, I'm sorry for David," said the winner. "As for me, it was nice have a victory like this.

"I'm here to improve every day, to enjoy every game, every point. It's hard to move well for me and to feel confident when you are touching the ball. But that's a normal thing."

Ferrer, playing with one knee taped and visited twice by the trainer, started poorly with a double fault and lost the opening game, setting a tone for Nadal.

Nadal, the four-time French Open champion who had to sit out Wimbledon because of his troublesome knees, faces a Thursday date with German Philipp Petzschner, who upset Spain's Tommy Robredo 7-6 (7/3), 7-6 (7/4).

"I'm very sorry it had to end like this," said Nadal, who saved six break points in the fourth game before losing serve, only to break the fading Ferrer again in the seventh game as the early end came.

"Philipp is a very strong player and I will have to play well to beat him. But I'm here to do that this week."

Ferrer said he came to the court with few expectations after experiencing pain in his left knee even before the match.

"I had problems in my knee and I could not really play. I prefer to relax for these few days and stand by for next week to Cincinnati."

Fifth-seeded Wimbledon finalist Andy Roddick opened against Russian Igor Andreev, with the American carving out a patchy 6-1, 7-6 (7/3) win.

"Not perfect, but, you know, obviously I'll take the win," said the world number five.

Roddick complained that the court in Montreal was even slower than last week in Washington, where he also reached the final.

And the constant varying of tennis ball brands from event to event has him annoyed.

"It's a slow center court, and the ball is not really moving too much," he said. "I didn't think Washington was overly fast, and it's pretty slow here.

"I still think that we shouldn't be changing tennis balls midsummer. That's just the height of not using common sense."

Washington champion and sixth seed Juan Martin Del Potro beat Czech Jan Hernych 6-2, 7-5.

Spaniard Juan Carlos Ferrero moved into a third-round showdown with world number three Andy Murray for the third time since June and will hope to reverse his fortunes after two defeats against the Scot.

Ferrero felled French 13th seed Gael Monfils 6-3, 7-6 (9/7) to notch his 30th victory of the season.

But the Spaniard lost to Murray at Queen's Club and a fortnight later in the Wimbledon quarter-finals.

"Playing Murray means that I'm playing well," said Ferrero. "It's going to be very tough. but I want this win.

The fate of Murray's run towards the number two ATP ranking could be in the hands of the veteran.

Murray needs to surpass the performance this week of Nadal to take over the second spot behind Switzerland's Roger Federer.

Unseeded Swiss Stanislas Wawrinka beat Kazak Andrey Golubev 7-5, 6-4 to reach a second match of the season against fellow Olympic doubles gold medallist Federer. Wawrinka defeated his good friend four months ago on clay in Monte Carlo.