ROME: World number one Rafael Nadal will play Novak Djokovic in the final of the ATP Rome Masters after their respective victories against Fernando Gonzalez and Roger Federer on Saturday.

World number three Djokvic is the reigning champion here and needs to retain his title or Britain's Andy Murray will overtake him in the world rankings, while Nadal claimed the crown in the three previous years.

Serbian Djokovic made the most of a rain break to transform his play and beat Federer 4-6, 6-3, 6-3 in a thriller.

He was trailing by a set and a break when the heavens opened to give him some much needed respite.

After a little more than an hour off court, Djokovic came back rejuvenated while Federer's game slowly crumbled.

The Swiss master hadn't even faced a single break point before the rain but was broken five times after it as his game gradually broke down.

He later blamed the rain for his defeat.

"Things were going well for me, I was playing him well and serving well when I had to and putting him under pressure so it (the rain) kind of definitely changed the momentum," he said.

"I mean, the rain delay came at a perfect moment for him because he came through a tough service game at 2-0 down.

"Instead of going 3-0, he goes 2-1 and then the rain comes, so he's got something positive to look at. "Then when he comes back conditions changed, so, sure, it helped him. But then again, who knows.

"He might have come back anyway and beat me in the end. He did well today to use the rain delay in his favor, that's for sure." The match had started in bright sunshine, during which time Federer had been at his dominant best and was in complete control.

Djokovic was regularly forced to save break points and at 4-4 Federer finally managed to break serve at the sixth attempt in the set - although in controversial fashion.

As Djokovic was about to hit a second serve at break point, a whistle from the crowd put him off.

That seemed to rattle the 21-year-old and in the ensuing rally he hit a wild forehand long to gift Federer the break.

Djokovic then glared long and hard into the crowd from where the whistle had come while fans around the stadium chanted "out, out, out!" Federer served out the set and then broke in the opening game of the second as Djokovic netted a backhand.

The number two seed led 2-1 when the rains came and held his first service game after them.

He had a chance for a double break and a 4-1 lead but after Djokovic saved that and held, the wind changed completely.

The Serbian broke back when Federer sent a backhand slice drifting over the baseline and he broke again for a 5-3 lead when Federer shanked a backhand off the frame.

Djokovic served out the set to love and looked to be in the ascendancy.

However, Federer regrouped and drew first blood in the decider when he broke for a 3-1 lead after a string of Djokovic errors including a nervous wayward forehand on break point.

But Federer then made three unforced errors to give the Serbian a 40-0 lead and a crosscourt forehand winner secured a break back.

After that Federer's game simply crumbled, particularly his backhand. He lost his next service game with a netted backhand slice and then threw away his final service game with another backhand error into the tramlines.

It was the first time Djokovic had beaten Federer on clay.

Nadal had few problems in despatching Chilean 12th seed Gonzalez and the Spaniard broke his opponent four times on the way to victory.

From the moment he opened up a 4-3 lead after a series of three breaks in a row, Nadal never looked back and romped to his 29th straight win on clay.