MADRID — Roger Federer and Rafael Nadal reached the quarterfinals of the Madrid Masters on Thursday with straight set victories.

The top-ranked Federer beat Swiss countryman Stanislas Wawrinka 6-3, 6-1 and second-ranked Nadal saw off big-serving John Isner of the United States 7-5, 6-4.

Defending champion Federer never looked troubled against Wawrinka, and appears to be shaking off the slip in form that had him lose in the semifinals in Estoril and the second round in Rome recently. In the quarterfinals he'll play Ernests Gulbis of Latvia, who beat him in Rome.

Isner, who reached the clay final in Belgrade last weekend, held his own against Nadal before losing his serve in the 11th game of the first set, during which he received treatment to his arm.

Nadal served out for the set and broke the American early in the second before holding his service for victory.

"It was a very dangerous and difficult match and I played well, and when I had chances with the return I took them," said Nadal. "For me it was a very important victory."

Nadal came into the Madrid Masters on the back of tournament wins in Monte Carlo and Rome. The 2005 champion and 2009 finalist hopes to extend the record for Masters titles of 17 he shares with Andre Agassi.

Another favorite to win the tournament, third-seeded Andy Murray, had little trouble beating Victor Hanescu of Romania 6-2, 6-1.

Two breaks of serve in each set saw the Scot stroll to victory, setting up a quarterfinal with David Ferrer, who beat Marin Cilic of Croatia 6-3, 6-2.

Murray hadn't won two matches in a row since Indian Wells in March and he was pleased.

"Hanescu isn't an out-and-out clay-court player so it was a different match than you normally get, but I felt comfortable," Murray said.

"I know that against the clay-courters I'll have to play more aggressively and will have to improve."

Earlier, Fernando Verdasco's 7-5, 6-3 third-round loss to Jurgen Melzer of Austria left only three of the top eight seeds in the tournament.

With the center court's retractable roof closed due to rain, the sixth-seeded Verdasco looked far from his best and had treatment on his right ankle after the first set.

Melzer broke early in the second set before Verdasco broke back for 3-3. Melzer took the next three games to clinch victory over Verdasco for the second time in seven attempts and reach his fifth quarterfinal this season.

A frustrated Verdasco said his ankle was hurting after he injured it in the previous round against Ivo Karlovic, although he said the match conditions also bothered him.

"I haven't played indoors for months and I've never had the opportunity to train here with the roof closed — I think it gave him the advantage," he said. "He's more of an indoor player than an outdoor player, which also went against me. The court also wasn't in the best condition, which made me miss certain shots that were very important."

Melzer will next play Nicolas Almagro of Spain, ensuring there will be at least one unseeded player in the semifinals. Almagro beat Juan Monaco of Argentina 6-4, 6-1.

In the women's third round, eighth-seeded Samantha Stosur of Australia beat Patty Schnyder of Switzerland 7-6 (3), 6-2 to set up a quarterfinal with Venus Williams.

"It's Venus so you have to expect a good match," Stosur said. "Clay probably isn't her favorite surface. We've played a few times and I've never been able to win so it's one of those times when I have to go out there and give it my best shot."

Seventh-seeded Jelena Jankovic of Serbia cruised through against Anabel Medina Garrigues of Spain, 6-2, 6-0, while Aravane Rezai of France beat Andrea Petkovic of Germany, 6-4, 7-6 (8).

Li Na of China beat Alona Bondarenko of Ukraine 6-3, 6-4 and Shahar Peer of Israel defeated Arantxa Parra Santonja of Spain 7-5, 6-2.