Rafael Nadal survived a battle of creaky knees against David Ferrer on Wednesday, the fellow Spaniard retiring hurt from their second round match at the Montreal Masters to gift the world number two a comeback win.

Sidelined for more than two months with tendonitis in both knees, Nadal's tender joints were in the spotlight for his first singles match since his shock loss to Sweden's Robin Soderling in the fourth round of the French Open in May.

But it was Ferrer's left knee that became the talking point after he abruptly retired when trailing 4-3 in the opening set.

Ferrer's retirement whisked Nadal into a third-round meeting with Philipp Petzschner of Germany, but the brief 37-minute workout answered few questions about the former world number one's own fitness.

"I need more days to have a real test but it was ok," Nadal said. "I tried everything 100 per cent but when you come back from injury, it's difficult to move well the first match.

"Everything is positive, every match, every point. Everything is helping me be ready as soon as possible to return to my level.

"I have another chance tomorrow to continue to improve."

Tennis fans got better value for money during the day session, when resurgent Spaniard Juan Carlos Ferrero defeated 13th seed Gael Monfils of France 6-3 7-6 to move into the third round.

American fifth seed Andy Roddick, another player enjoying a career revival this season, also advanced with a tidy 6-1 7-6 win over Russian Igor Andreev.