Women's top seed Serena Williams and defending champion Maria Sharapova also stayed on course for a potential meeting in the final as they progressed to the last four with wins over Carla Suarez Navarro and Caroline Wozniacki respectively.

Nadal has yet to win a European clay court tournament this season after defeats to Novak Djokovic at the Monte Carlo Masters and Fabio Fognini at the Barcelona Open last month.

However, he remains the heavy favourite in the Spanish capital in the absence of world number one Djokovic and will continue his quest for a fifth Madrid title against Bulgaria's Grigor Dimitrov on Friday.

Dimitrov disposed of Stan Wawrinka in the last-16 7-5 (7/5), 3-6, 6-3 just as he did at Monte Carlo.

"Dimitrov is a very complete player, he is one of the best in the world," said Nadal.

"He has already won three matches here, so he is at a good level again. He played very well against Wawrinka and (Fabio) Fognini. Hopefully tomorrow I will be ready to compete well against him."

Tomas Berdych continued his impressive start to the clay court season as he also marched into the quarter-finals with a 7-5, 6-2 win over Jo-Wilfried Tsonga.

The Czech faces John Isner in the last eight after the American beat Roger Federer's conquerer Nick Kyrgios 6-3, 6-7 (7/9), 6-4.

Seventh seed David Ferrer won the battle of the Spaniards as he came from a set down to beat Fernando Verdasco 5-7, 6-4, 6-4.

Williams extended her unbeaten record this season to 24-0 as she swept aside Spain's Navarro 6-1, 6-3.

The 19-time Grand Slam champion had to save three match points in overcoming two-time Australian Open champion Victoria Azarenka on Wednesday, but had no such trouble as she maintained her record of never having dropped a set against Navarro in their six meetings.

Sharapova also reached the last four for a third consecutive year with a 6-1, 3-6, 6-3 win over Wozniacki.

The Russian showed no ill effects early on from her marathon win over Caroline Garcia on Wednesday as she raced through the first set.

Wozniacki battled back to take the second set, but unlike in their previous two meetings at the US Open and the end of season finals in Singapore, it was Sharapova who emerged victorious in the decider to set up an all-Russian semi-final with Svetlana Kuznetsova.

"I think this was an important match for me, and also an important match to see where my level was and how I can withstand that physicality of a match against her," said Sharapova.

"It's obviously a tournament I want to do well in. I feel like it's almost the beginning of my clay court preparation towards the French Open."

Kuznetsova battled past Lucie Safarova 5-7, 7-6 (7/5), 7-6 (7/3) in over three hours on court to make her first semi-final since last July in Washington.

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