PARIS (AFP) - Top seed Roger Federer set up a French Open quarter-final against old rival Fernando Gonzalez on Monday but he was below par in a rain-hit 6-4, 7-5, 7-5 win over Frenchman Julien Benneteau.

Gonzalez had looked impressive earlier in the day when he swept past the final American, Robby Ginepri, in straight sets 7-6 (7/4), 6-3, 6-1.

French representation in the last eight was assured when former world junior champion Gael Monfils defeated Ivan Ljubicic of Croatia 7-6 (7/1), 4-6, 6-3, 6-2 in a bruising battle of big servers.

He will play the winner of the tie between fifth seed David Ferrer and Radek Stepanek of the Czech Republic with a semi-final berth going to the winner.

Federer has dropped just one set en route to the last eight, but he will have cause for concern over how he struggled to kill off his lowly-ranked opponent.

"I couldn't serve it out the way I wanted to in the first and second sets, but I felt okay out there," Federer said. "But it was tough conditions with the rain delay.

"I didn't think I had my best serving day today unfortunately. But the last three (games) have been good so I hope the next one is going to be okay again as well."

The unseeded Benneteau had played more sets than any other player to get the last 16 (14) and he was not expected to pose any problems for the world No. 1 who won their only previous meeting in straight sets in Cincinnati last year.

But in each of the first two sets he broke Federer's serve when trailing 3-5 only to lose both of them by 6-4 and 7-5.

At that stage heavy rain brought an abrupt end to proceedings and it took ninety minutes before they got back onto a packed Philippe Chatrier Centre Court.

With warm sunshine replacing the gloomy skies that marked the earlier action, Federer again went a break up to lead 3-1, but again Benneteau battled back to level at 3-3.

The Swiss maestro was finding it hard to put away his world-ranked 55th opponent, letting slip a match point at 5-4 up but two games later he finished it off with a smash at the net.

Benneteau said it had been an "exceptional experience playing against Federer on the centre court.

"But I was always behind, that was the problem today and I had few opportunities."

The 26-year-old Federer is bent on winning the only Grand Slam title that has eluded him having lost to Rafael Nadal here in the last three years, including the last two finals.

He came into Paris after a poor season by his own high standards having lifted just one title at Estoril and losing seven times, twice to Nadal on clay.

Big-hitting Gonzalez matched his best ever Roland Garros performance by defeating Ginepri.

The lone South American survivor in the tournament's fourth round last got to the final eight in 2003 when he lost in five sets to eventual champion Juan Carlos Ferrero of Spain.

Ginepri's run to the last 16 had been entirely unexpected as he had lost in the first round in his five previous appearances.

The American held his own for a set and a half but he struggled to cope with the Chilean's trademark sledgehammer forehand and his head visibly went down when he fell two sets down.

Gonzalez powered away to reach a Grand Slam quarter-final for the first time since the 2007 Australian Open when he eventually lost in the final to Federer.

"I think it's very exciting for me to come back to this tournament," he said. "I have good memories from Australia and my dream is to win one Slam.

"Last year I remember I had many difficulties playing on clay. I could play all right on very fast surfaces but here at Roland Garros, on clay, it was more difficult. But this year it is okay.

Ginepri paid tribute to Gonzalez saying his forehand was a potent weapon and one of the best in the game.

"Tough conditions out there for me, " he said. "Never really gave myself a chance, but Fernando's game was very solid and his game plan was better than mine."

Monfils kept the home flag flying after four of his compatriots had crashed out in the fourth round.

Back to full fitness after a succession of injuries, the 21-year-old Parisian slugged it out with 29-year-old Ljubicic for just short of three gruelling hours before finally wearing him out in four sets

"It's incredible," he said. "I am so moved and what is to follow will be just as beautiful."