Federer was gifted too many points by his French opponent
Top seed Roger Federer and defending champion Rafael Nadal moved into the quarter-finals of the Monte Carlo Open with comfortable straight sets wins.
After struggling to overcome Ruben Ramirez Hidalgo in his previous match, Federer had a far easier time of it in beating France's Gael Monfils 6-3-6-4.
He broke serve three times as Monfils was guilty of too many unforced errors.
Three-time champion Nadal was even more convincing as he saw off Spanish compatriot Juan Carlos Ferrero 6-4 6-1.
Nadal is searching for a fourth straight title in Monaco and his first since winning in Stuttgart last July.
He and Ferrero played an intense first set but Nadal made the decisive break and though they swapped breaks in the second, Nadal never look troubled.
The world number two faces fellow countryman David Ferrer next.
Ferrer, the world number five, beat Janko Tipsarevic of Serbia 6-4 6-0, breaking serve six times to wrap up the one-sided match in just 67 minutes.
Russian Igor Andreev booked his place in the quarter-finals, defeating Nicolas Almagro 7-5 4-6 6-4.
Though not at his best, Federer had enough consistency to overcome Monfils.
He was broken in the third game but hit back to level at 2-2, breaking serve again to establish a 5-3 lead.
Federer broke his opponent in the third game of the second set and was leading 4-2 when Monfils saved three break points.
The world number one set up match point with a perfectly weighted drop shot that left Monfils stranded.
He won on his second match point with a service winner that curled away from the Frenchman.
My forehand worked well," Federer said.
"I was just happy, after yesterday, [his struggle against Ruben Ramirez Hidalgo] playing so well. Today was fine again. It's good I reacted so well after yesterday's tough match."
Federer will now play sixth seed David Nalbandian.