In men's first-round play, ninth-seeded John Isner beat Russian qualifier Teymuraz Gabashvili 7-6 (8), 6-4, with the American securing the only break in a match heavy on baseline groundstrokes.

Kei Nishikori followed up his Barcelona Open triumph with a 6-4, 6-4 win against Ivan Dodig of Croatia.

Nishikori said working with former French Open champion Michael Chang boosted his confidence on this surface as he won his first career clay title in Barcelona.

"I did well last week in Barcelona and I'm getting better on clay, so hopefully I can go further this week," the 12th-ranked Japanese player said. "There was just one bad game, on my serve at 3-2 in the second set. Otherwise, it was an almost perfect match."

Jo-Wilfried Tsonga beat Edouard Roger-Vasselin 6-3, 4-6, 6-3, while Gilles Simon emerged from another all-French matchup, after Benoit Paire retired, to play Roger Federer next.

Stanislas Wawrinka, who is looking to follow-up his Monte Carlos Masters triumph, opens in the Spanish capital against Dominic Thiem after the Austrian beat Dmitry Tursunov of Russia 6-4, 6-2.

Other winners were Mikhail Youzhny of Russia, Jarkko Nieminen of Finland, and Spanish players Fernando Verdasco and Feliciano Lopez.