By Alex Perry BBC Sport at Wimbledon

I am the kind of guy who is going to go for risks, that's just he way I play Mark Philippoussis Photos from the marathon match Each set as it happened

Mark Philippoussis rolled back the years to knock out Andre Agassi in a marathon battle on Court One.

The Aussie, who was once told he would never play again because of a severe knee injury, was back to his fearsome best on serve, delivering an unbelievable 46 aces during an epic encounter lasting well over three hours.

Agassi had recovered from losing the opening set to go two sets to one up by storming through a third set tie-break.

But the unseeded Philippoussis fought back impressively and crucially broke once in both the fourth and fifth sets to close out a thrilling 6-3 2-6 6-7 (4/7) 6-3 6-4 victory.

Watch fourth round highlights(Modem)

He will now face Germany's Alexander Popp in the last eight, and must be considered a real threat for the title.

Watch fourth round highlights(Broadband)

Afterwards, Philippoussis said that he and his father had started from scratch as they attempted to rebuild his game following three operations on his left knee in 14 months.

"When things aren't going your way and you're struggling I think the best thing to do is go back to basics," he said.

"That's the way I've been training - doing the things I used to do when I was younger."

The Australian also felt going for broke at every opportunity had helped give him the edge.

"I am the kind of guy who is going to go for risks, that's just the way I play.

"I'm not the kind of guy who is going to think about it a lot - I play with instinct."

It's the greatest tournament in tennis Andre Agassi on Wimbledon

Philippoussis started well as he attempted to overturn a six-match losing streak against Agassi, dropping just four points on serve as he took the first set.

Double faults and unforced errors looked to have handed Agassi the initiative, with the world number one breaking twice in the second set to level things up.

And when Agassi romped through the third set tie-break with some blistering forehand passes, he was on course for the quarter-finals.

But Philippoussis was in no mood to give up, and finally broke through at the start of the fourth set.

Agassi, the 1992 champion, had chances to break back at 2-4, but Philippoussis recovered from 0-40 down with aces number 31 and 32, and then duly served out with ace number 35.

Have Your Say Will it be Henman's year?

Three more aces helped Philippoussis save two break points in the sixth game of the decider before he gained the crucial break of serve thanks to a wild Agassi backhand.

And despite Agassi's best efforts from the other side of the net, the 26-year old held his huge serve together, and showed impressive stamina to claim a memorable victory.

The world number one said afterwards that he fully intends to be back for another stab at the Wimbledon title next year.

"This is the place to be," he said. "It's not easy to win Wimbledon, for it to happen again would be an amazing thing."