HAMBURG, Germany: Top-seeded Rafael Nadal toiled to beat Jiri Vesely 6-4, 7-6 (2) to reach the Hamburg Open quarterfinals on Thursday.

Nadal's quarterfinal opponent will be fifth-seeded Pablo Cuevas of Uruguay, who outlasted Jerzy Janowicz of Poland 6-3, 4-6, 6-2.

Nadal appeared in trouble when he dropped his serve for 4-4 in the second set. But he broke right back and served for the match, only to commit a double fault at match point. He served another double fault to drop the game, but Vesely could not take advantage and Nadal cruised through the tiebreaker, winning the match when Vesely netted a backhand.

Nadal is playing in Hamburg for the first time since he won the clay-court event in 2008.

Andreas Seppi of Italy also reached the quarterfinals by beating Florian Mayer of Germany 4-6, 6-2, 6-3.

Roger Federer pulls out of Montreal tournament

Roger Federer pulled out of next month's Rogers Cup hard-court tournament on Wednesday.

A spokeswoman for Tennis Canada, Valerie Tetreault, wrote in an email to The Associated Press that Federer "wants to make sure he will be (in) top shape for" the U.S. Open, the year's last Grand Slam tournament, which begins Aug. 31.

"I am disappointed that I won't be playing in Montreal because it's a tournament and a city that I really enjoy and has incredible fans," Federer said in a statement released by Tennis Canada. "I hope to be back in the future."

Federer, owner of a record 17 major championships, has not competed since losing to Novak Djokovic in the Wimbledon final on July 12.

Federer, who turns 34 on Aug. 8, won the Rogers Cup twice, in 2004 and 2006, and he was the runner-up a year ago.

"We are obviously disappointed to have Roger withdraw as it is always a privilege to watch him play," tournament director Eugene Lapierre said in a statement. "We also understand his decision because, above all, he has always been very loyal to our event and we would love to see him play tennis for many more years to come."

Play begins Aug. 10 in Montreal. Federer will be replaced in the main draw by Jerzy Janowicz, a semifinalist at Wimbledon in 2013.

Del Potro uncertain over return

Injury-plagued former US Open champion Juan Martin del Potro admitted Thursday that he still cannot pinpoint a return to the tour after undergoing a fourth wrist operation.

The 26-year-old del Argentine has played in just two tournaments in 2015 after managing only four in 2014 while his world ranking has plummeted to 570.

Del Potro underwent his latest wrist surgery in March.

"The hardest moments of my career are gone, those in which I didn't know what I would do next," del Potro, who parted ways with long-time coach Franco Davin last week, wrote on Facebook.

"I've already told you the discomfort of being unable to do what I like and the suffering of watching tennis on TV. Today is a different story. I have great expectations for a new stage that began this week.

"Today I am more committed than ever to trying to come back. No more doubts or question marks. A new career for me starts today."

The 2009 US Open champion added: "This week I began rehab and did some light workout. While I start from scratch, I've been on a diet to maintain weight.

"I don't know how long it will take, I do not know at what level I will play, but I hope to be with you on the tour again."