* Federer through to third Rome final
* Nadal beats Berdych 6-2 6-4
* Serena sees off qualifier Halep (Adds Federer quotes)
By Eric Salliot
ROME, May 18 (Reuters) - Roger Federer will meet great rival Rafa Nadal in the Italian Open final after the Swiss held off a spirited challenge by unseeded Frenchman Benoit Paire on Saturday.
The 7-6 6-4 scoreline suggested a routine victory for the world number three, but the 24-year-old Paire was a break up in the first set and held three mini breaks in the tiebreak before being let down by poor shot selection.
The second set was more straightforward for Federer, into the Rome final for the third time and first since 2006, as he wrapped up victory in just under 90 minutes.
Nadal had earlier beat Czech sixth seed Tomas Berdych 6-2 6-4 with a dominant performance that he described as emotional after a long injury absence which saw him return to court in February after seven months off with a knee problem.
The Spaniard has won six titles since returning, while Federer is yet to register a title in 2013.
"For me it's already a good tournament. He (Nadal) is the favourite but he's near the end of a long claycourt season, it may be my chance," Federer told reporters.
Nadal, the sport's dominant claycourt player was at his aggressive best in dismantling the heavy hitting Berdych, breaking in the first and fifth games of a one-sided first set before clinching a decisive advantage in the ninth game of the second.
Nadal wrapped it up when his opponent sent a backhand return long and then said he could not have hoped to be playing better after his lengthy layoff.
"I am feeling better physically," the 11-times grand slam winner said in an interview with Spanish television broadcaster Teledeporte.
"These are emotional moments for me as I think I have managed to turn around a situation in which after many months of doubts I am able to play at a level that I would not have dreamed of four months ago."
Serena Williams crushed Romanian qualifier Simona Halep 6-3 6-0 to book her place in the women's final and extend her winning streak to 23 matches.
World number one Williams, who is chasing a fourth consecutive tour title, will face Victoria Azarenka in Sunday's final after the third seed beat last year's French Open finalist Sara Errani 6-0 7-5.
Williams's unbeaten run has included title successes in Miami, Charleston and Madrid and she is chasing a first Rome title since 2002, the year she won her only French Open.
"I love the clay. I haven't had many wins at Roland Garros but I do love it," Williams told reporters.
"I was unhappy with some things today. I want to do well here as well as (in Paris)."
Williams' opponent was playing her first top-level semi-final and was bidding to become the first qualifier to reach the final in Rome.
Halep scored an early break of serve for a 2-1 lead in the first set but then wilted, winning just one more game as 15-times grand slam singles champion Williams steamrollered her way into the final. (Writing by Toby Davis in London; additional reporting by Iain Rogers; Editing by John Mehaffey and Alison Wildey)