Injury-Proned Rafa Nadal Back in Form to Crush France's Gael Monfils - - Advances to Quarter Finals of US Open

The Spaniard, who is on his way back from a serious knee injury, has also had an abdominal problem but showed no sign of it in Tuesday's night match.

Nadal showed great reserves of strength to win 6-7 (3-7) 6-3 6-1 6-3 and set up a match with Fernando Gonzalez.

Juan Martin del Potro and Marin Cilic also won to set up a quarter-final tie.

In the final match on Arthur Ashe Stadium, Monfils edged a high-quality first set in the tie-break after failing to serve out at 5-3, with his huge serving and heavy forehands taking him through.

But after some exuberant celebrations, the Frenchman soon found that Nadal was going nowhere and had retained his incredible stamina.

After the pair swapped breaks midway through the second set, Nadal broke again in a breathless eighth game of punishing rallies that left his opponent exhausted.

Monfils could only win four more games as Nadal hit the kind of form that has taken him to six Grand Slam titles, and suggests he could complete the set with his first US Open victory.

And afterwards he described the conditon of his knees as "very good" before adding: "I'm very happy now after the last two matches I played.

"I had a few problems in those but now I'm in the quarter-finals for the third time in my career here and I'm really really happy.

"I'm here just to play my best and try to enjoy my comeback. For me to come back here and play in the quarter-finals is very big, a big result for me, so very happy."

Chile's Gonzalez, seeded 11th, beat seventh seed Jo-Wilfried Tsonga of France 3-6 6-3 7-6 (7-3) 6-4 in a pulsating match on Louis Armstrong Stadium.

Gonzalez gave his racquet to a woman in the crowd at one point as he struggled to control his temper early on, but the 29-year-old stormed back and took control in the third set tie-break.

Trailing 5-4 in the fourth set, the pressure became too much for Tsonga and he double-faulted twice as he handed over the game and the match.

"In my first match here I didn't feel like I really wanted it," said Gonzalez. "Today I feel much better, I play really good tennis again. Hopefully I can continue this week."

Sixth seed Del Potro proved too strong for Juan Carlos Ferrero as he moved into the last eight with a 6-3 6-3 6-3 win.

The Argentine's big serve was the foundation of his victory as he served 22 aces on his way to victory, without ever being broken.

Del Potro lost to Murray in the quarter-finals last year but has since risen to sixth in the rankings and narrowly lost to Federer in five sets in the French Open semi-finals.

"Being in the quarters, it's important," said Del Potro. "But it's a big difference past the quarters to the semis and then through to the finals.

"I was so close in the French Open to reach the final and to beat Roger. Here I have another chance to be better and I will try to go the semis. If I lose I still had a good tournament."

The 20-year-old's improved serve has been a major factor in his success, along with his power off the ground, and he made 44 winners as he dominated Ferrero.

"When you play somebody like this, you feel a lot of pressure with your service games," Ferrero said afterwards.

"I think he's playing a level to win a Grand Slam. I think he can play against anybody here. He has to play against Cilic right now, I think this is a chance for him to get into the semis."

Croatia's Cilic, the 16th seed, beat Britain's Andy Murray 7-5 6-2 6-2 in the day session on Arthur Ashe Stadium to reach his first Grand Slam quarter-final.

"Now that I don't have this blockade in my head, I can focus on winning other matches," said the 20-year-old. "I'm feeling tremendously happy. It's the biggest result for me so far."

In the other half of the draw, defending champion Roger Federer, Robin Soderling, Novak Djokovic and Fernando Verdasco are already through to the last eight.