Former world number one Roger Federer was beaten 6-4, 7-6 by Gael Monfils in the third round of the Monte Carlo Masters on a bad day for the Swiss which also saw Stanislas Wawrinka exit.

Defending champion Wawrinka put up only token resistance as his game fell apart in a 55-minute 6-1, 6-2 rout at the hands of Bulgarian Grigor Dimitrov on Centre Court.

Third-seed Rafa Nadal, who ruled in Monte Carlo from 2005-12, overcame John Isner, but was given a fright.

The Spaniard had to save two set points in the opening set and then found himself pegged back before advancing to the last-eight 7-6, 4-6, 6-3.

Nadal broke decisively in the fourth game of the third set to set up a meeting with Spanish fifth seed David Ferrer or Frenchman Gilles Simon.

Dimitrov will face Monfils in the quarter-finals after the French showman, decked out in green and black stripes, saw off second seed Federer in a high-quality contest.

"It was not the best end to the match," Federer told reporters. "I should have done better with the break up in the first. I think I did a good job to hang around the second set. I also had chances of my own.

"I never felt like things were really happening the way I wanted them to be going during the whole match."

Results:

Rafa Nadal (Spain) beat John Isner (U.S.) 7-6(6) 4-6 6-3

Marin Cilic (Croatia) beat Jo-Wilfried Tsonga (France) 6-3 7-6(5)

Tomas Berdych (Czech Republic) beat Roberto Bautista (Spain) 7-6(7) 6-4

Gael Monfils (France) beat Roger Federer (Switzerland) 6-4 7-6(5)

Milos Raonic (Canada) beat Tommy Robredo (Spain) 6-3 3-6 6-3

Grigor Dimitrov (Bulgaria) beat Stanislas Wawrinka (Switzerland) 6-1 6-2

Source: Agencies