Nadal still has not lost at Wimbledon since 2007

Rafael Nadal was stretched to five sets for the second match running at Wimbledon before finally booking his place in the fourth round.

The world number one needed three hours and 45 minutes to beat Philipp Petzschner 6-4 4-6 6-7 (5-7) 6-2 6-3.

But the 2008 champion was far from convincing, and perhaps more worryingly, needed treatment on court for elbow and knee injuries.

He will have a day to recover before facing Paul-Henri Mathieu on Monday.

Under normal circumstances, Mathieu would not be expected to test the world number one, but Nadal's body appears to creaking under the strain of his astonishing run of four straight titles on clay, including the French Open.

Nadal relieved after 'tough' match
The world number one told BBC Sport he hoped to be "fine" for Monday, but he said later: "I am a little bit scared about the knee."

Nadal, who missed Wimbledon last year as he struggled with tendonitis in both knees, went on to explain that he had had successful treatment on his left knee after winning the Monte Carlo title in May, but had not yet had time to receive the same attention to his right knee.

"I know the knees are not 100% recovered," said the 24-year-old, who did at least play down the problem with his left arm.

"But I can finish the match today and we'll see how it is tomorrow. It's not something new, I know what I have to do to recover the knee. I just didn't have time."

Injuries were not the only source of concern for Nadal on Saturday.

In the fifth set, the umpire, who had already spoken to the second seed at an earlier changeover, gave Nadal an official warning for receiving coaching from his uncle Toni - prompting a furious reaction from the Spaniard.

"I told the umpire we're going to talk to the supervisor later, and I will," said Nadal. "Toni wasn't giving me any tips, only supporting me. When he gave me the warning, Toni was saying 'positive'."

Nadal might be better served figuring out how to deal with the all-out aggression demonstrated by Robin Haase, who took him to five sets in his previous match, and 33rd seed Petzschner.

Petzschner's previous best Grand Slam run came last year when he also reached the third round, and he needed two five-set matches to book his meeting with Nadal.

But the German served magnificently on Saturday, particularly under pressure, and clubbed forehands past Nadal on a regular basis.

"This match was very difficult for me," admitted the world number one, who watched 25 aces come past him.

"Philipp was serving unbelievably all match and probably I changed the strategy a little bit in the fourth."

Nadal broke serve in the opening game as Petzschner came to terms with the rarefied atmosphere of Centre Court.

But the world number one was unusually profligate and nine break points came and went before he broke again in game four of the fourth set.

In between, Nadal played an alarmingly error-strewn game at the end of the second set to allow Petzschner to level the match.

And trailing 5-4 in the third, the Spaniard called the trainer for the first time to receive treatment to an apparent left elbow injury.

He emerged to hold serve and then earn a break point in the next game, but Petzschner, not for the first or last time, saved it with a huge first serve.

The set then went to a tie-break and a packed Centre Court crowd watched in amazement as Petzschner, not Nadal, stamped his authority on it.

Having recovered an early mini-break, the German put away a stunning low volley before Nadal dumped a routine forehand into the net.

Petzschner's adrenalin was really pumping when he fired a huge forehand into the corner to bring up three set points and not even a broken string, necessitating a change of racquet, could prevent the underdog taking a shock two sets to one lead.

The trainer came back onto court and was quickly sent packing by Nadal, but the Spaniard called for attention again at 2-1.

This time, it was his right knee which seemed to be the problem, and with his previous knee trouble, his fans would have really been sweating.

Nadal, though, came out fighting and broke serve in the very next game, and he defied his knee problems when he scrambled out wide and bent low to whip a gorgeous forehand down the line as he moved into a 4-1 lead.


Nadal was furious at receiving a warning from the umpire
The trainer was out again at the next changeover, but by that time, Petzschner was having his own physical problems, the result of his arduous journey to the third round, and Nadal was able to seal the set with some ease.

An increasingly busy trainer now attended to Petzschner, and with Nadal's greater experience in Grand Slam play, the Spaniard always looked likely to take the fifth set.

So it proved, but not before his patience was severely tested by the umpire's warning in the fifth game.

However, leading 4-3, Nadal smacked a sensational forehand return past a stunned Petzschner as he earned the crucial break before serving out another hard-earned win.

But a second five-set battle, coupled with his physical problems, will have given hope to those, including fourth seed Andy Murray, on his side of the draw.

After Mathieu, Nadal could face the dangerous Robin Soderling, before a possible semi-final against Murray.

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