Rafael Nadal forced to hit big in his match with Juan Martin Del Potro. [Source: Wimbledon.com]

Champion and top seed Rafa Nadal feared his Wimbledon was over when he sustained a mystery foot injury yesterday but he fought through the pain to overcome awkward Argentine Juan Martin Del Potro and advance to the quarter-finals.

The Spaniard looked in danger of having to withdraw after receiving lengthy treatment at 6-6 in the first set but gritted his teeth to take the subsequent tiebreak en route to a battling 7-6 3-6 7-6 6-4 victory.

"I thought I'd have to retire," Nadal said of the problem that needed 10 minutes of on-court attention.

"I felt something very strange. I don't know what the problem is yet, I felt that I had broken my foot, I felt terrible.

"Some pain stayed with me for the match but the tape changed probably the position of the foot and the distribution of the power so I was able to continue."

The injury was just one of many talking points from one of the best matches of the tournament with Del Potro proving more than a dangerous floater as he continues his recovery and climb back up the rankings following wrist surgery.

There was nothing between the two players in a first set littered with crunching forehands -- though Nadal was unhappy to be given a time warning for his tardy serve preparations -- but things looked worrying for the Spaniard before the tiebreak when he needed treatment for the injury from the physio and doctor.

He eventually returned to the fray but looked tentative as Del Potro quickly led 3-0 with a mini-break. However, Nadal, channelling all his anger and frustration into his racket head, crashed his way back to lead 4-3.

Del Potro hit back with two mini-breaks but Nadal showed all his fighting qualities to come back again and took the tiebreak 8-6 when Del Potro double-faulted.

The Argentine, aiming for his first grand slam quarter-final since his 2009 US Open victory, continued to look the more consistent server but even he was reduced to clapping his opponent after one miraculous Nadal recovery shot when the Spaniard faced break point.

Del Potro did break in the eighth game, though, and took the set after getting the better of an exchange of drop shots that had the Centre Court crowd drooling.

In the third set it was Del Potro's turn to need treatment after he hurt his left thigh when he slipped on the base line but he too recovered fully to take the set to another tiebreak, only for Nadal to win it.

It was captivating stuff, both players unloading hugely powerful groundstrokes and finding seemingly impossible angles, but the match turned decisively Nadal's way when he broke for the first time in the fifth game of the fourth set.

The Spaniard then showed steely nerve to hold serve in the next game after trailing 0-30 and eventually completed victory in almost four memorable hours.

In the last eight he faces American Mardy Fish, who he has beaten in all five previous meetings, but he said he was still concerned about the injury, which will be scanned later last night or this morning.

"I'm worried, for sure," he said. "I'm going to do the MRI and we'll see what's going on.

"He (Fish) is playing at a very, very high level. He's very dangerous player, so I will try my best to be very competitive on Wednesday.

"I need be at my 100 percent. If not it's going to be impossible against him so I have to recover."