Having taken five days to get past Robin Soderling and five sets to see off Mikhail Youzhny, Rafael Nadal must have felt he was overdue some luck en route to his second Wimbledon final.

That luck duly arrived on Court One on Saturday, when Nadal was spared another potential epic against fourth seed Novak Djokovic, who was forced to retire at 4-1 down in the third set with a painful left foot blister.

Djokovic, feeling the effects of his five-hour last eight win over Marcos Baghdatis yesterday, gallantly took the first set 6-3.

But after hobbling through a second set which Nadal won 6-1, the premature ending was inevitable.

Nadal said: "I'm sorry for him because it's tough getting the semi-finals playing good tennis, and then to get a match like yesterday and have to

retire, that is tough for everyone.

"I don't feel bad. I've played two tough matches in five sets, and the other ones I have won in three sets.

"I lost a set today but I only had to play three sets, so I feel good physically for tomorrow."

Djokovic had already had physical problems having called the trainer in another previous five-set win over Lleyton Hewitt due to a back strain.

He put them aside to break the Spaniard in his opening service game of the match.

But from the moment Nadal slammed home a volley at the net to end a thrilling rally and break Djokovic early in the second set, the course of the match changed inexorably.

Increasingly, the Serbian's movement on the baseline was restricted, and although he continued to match Nadal with the power of his driving ground-strokes he was invariably coming off second best at the end of the gruelling exchanges.

After extensive treatment during a medical time-out at the end of the second set, Djokovic saved two break points to hold serve at the start of the third, but a feeble netted forehand saw him broken next time around.

When Djokovic, by now clearly limping, double-faulted and netted another forehand to go 4-1 behind, he approached Nadal at the changeover and conceded the match.

Djokovic explained a blister sustained during his win over Baghdatis had become infected, and painful enough to make him seriously consider whether to take to the court at all.

"I didn't sleep during the night because there was a lot of bleeding and I was barely walking this morning," said Djokovic.

"I wanted to avoid forcing the injury and making it more serious for the future.

"It was not only that. It was also my back which was a problem over the last couple of days and basically all my body.

"I'm really exhausted. Everybody is human and it's natural to feel like that."

Nadal's thoughts immediately switched to the challenge posed by Federer, against whom he performed creditably during a four-set defeat in last year's final, their only previous meeting on grass.

The 21-year-old, who has beaten the world number one in two of their three matches this year, all on clay, believes another year of experience ought to stand him in good stead.

"A lot of things have changed and I am playing so much better than last year," said Nadal.

"I am sure he is the favourite but if I continue playing my aggressive tennis I will go onto court believing in victory.

"Anyway I know I have to improve. If I want to win here any day I have to improve my volley, my slice, my aggressive game.

"I have to improve everything but I am just 21 years old."