Federer, Nadal press on

World number one Federer cruised into the quarters, ending the adventure of hometown qualifier Benjamin Balleret 6-3 6-2.

In contrast, world No. 2 Nadal struggled for one hour and 37 minutes to overcome a strong challenge from unheralded Belgian Kristof Vliegen.

The mighty Spaniard, still far from his best form on clay, broke his opponent's serve early in the first set and midway through the second to wrap up the game 6-3 6-3 on his first match point.

Nadal will play Argentina's Guillermo Coria, who also struggled in his third-round 6-7 (5-7) 6-4 6-3 victory over Germany's Nicolas Kiefer.

After losing the first set, the tournament's sixth seed came back from three games down in the second to defeat the German.

Spain's Tommy Robredo took his time to beat World No. 3 David Nalbandian 7-5 1-6 7-5 to advance to the quarter-finals of the Monte Carlo Masters on Thursday.

In the surprise result of the day, 15th seed Robredo defeated third seed David Nalbandian of Argentina 5-7 6 1 7-5 after more than three hours on the clay court.

Robredo will meet Argentine seventh seed Gaston Gaudio, who beat Italian qulifier Alessio Di Mauro 6-4 6-3.

In the day's early match, David Ferrer battled past Juan Carlos Ferrero 6-1 6-7 6-3 in an all-Spanish baseline duel to reach the last eight of the Monte Carlo Open on Thursday.

Ferrer, seeded eighth, eased through the first set in 24 minutes before 11th seed Ferrero, winner of the tournament in 2002 and 2003, clinched the second set 7-5 in the tiebreak.

The 2003 French Open champion could 0not match Ferrer's powerful ground strokes in the third set. He saved a match point at 5-2 before winning the game, but still bowed out on Ferrer's serve after two hours 21 minutes.

In the quarter-finals, Ferrer will face world number one Roger Federer who eased past Monaco qualifier Benjamin Balleret 6-3 6-2.

"I did what I could and never felt ridiculous but it was a bit difficult at the end," Balleret said.

Balleret recorded the win of his life in the second round when he ousted Sebastien Grosjean, France's number one and the 13th seed.

Grosjean retired with a back injury when Balleret was leading 4-6 7-5 3-2. He was rewarded by a match against Federer who took only 55 minutes to win.

"It was a fabulous experience," the 23-year-old said. "It's even better because I have the feeling that Roger didn't take me lightly and played his real game."

Federer swept aside Ferrer 6-1 6-4 in the semi-finals of the Miami Masters three weeks ago.

Ivan Ljubicic (Cro) also advanced to the quarters, easily defeating Frenchman Gilles Simon 6- 6-2. The tournament's fourth seed will face the winner of Robin Söderling (Swe) versus Fernando Gonzalez (Chi).