Ferrer made a superb recovery in the opening set to help take the win

Spaniard Robredo, the fifth seed, lost 1-6 6-3 6-2 to 10th seed Tomas Berdych of the Czech Republic.

Seventh seed Ljubicic lost 6-3 6-7 (5-7) 7-5 to Frenchman Richard Gasquet.

Spain's David Ferrer was a 7-5 6-4 winner over Serbian teenager Novak Djokovic, the sixth seed and winner of the Miami Masters earlier this month.

Ferrer recovered from 4-1 down in the first set and will next face Roger Federer who eased past Korea's Hyung-Taik Lee 6-4 6-3 to reach the quarter-finals for the third year in a row.

The world number one set up match point with a serve-and-volley winner and then earned the victory when Lee hit a powerful backhand long.

Federer admitted his timing had been off in the early stages.

"I was just shanking a lot and not able to keep the ball in play, " he said. "But once I was able to do that, I was in total control. So I never felt too worried."

Monte Carlo champion Rafael Nadal remained on course for another clash with Federer by beating hammering Belgian Kristof Vliegen 6-1 6-1.

The victory extended the Spanish second seed's record winning streak on clay to 64 matches.

He was last beaten on his favourite surface by Igor Andreev in Valencia in 2005.

Nadal, who scored 21 unanswered points in the second set, said: "I'm happy with my level - I played a very, very comfortable match."