Andre Agassi scored a dramatic 2-6, 6-3, 6-4 victory over Spain's Juan Carlos Ferrero at the ATP Masters Cup on Wednesday, clinching the year-end number one ranking for American compatriot Andy Roddick.

Roddick was not at the Westside Tennis Club to thank Agassi personally but he will owe the eight-time Grand Slam winner a big pat on the back the next they meet for his stunning performance against the French Open champion.

"Andy had number one in his hands the whole week," said Agassi who only once in his long career finished the year with the number one ranking beside his name.

"But, you know, glad to help ... I aim to please.

"For him to dominate the hardcourt season the way he did is incredible. I did that in 1995 and it just took a lot out of me.

"He's proven himself to be number one over the greatest players in the world. So he has a lot to feel proud about."

While Roddick did not attend the match, the 21-year-old U.S. Open champion quickly responded to the news issuing a statement soon after the contest was completed.

"I'm incredibly honoured to finish the year as number one but I'm probably more proud to be the sixth American," Roddick said.

"It's hard to reflect on what a year this has been but I'm incredibly fortunate to be playing at home in the United States."

While the win meant the world to Roddick it was also key for Agassi, levelling his Blue Group record at 1-1 and keeping him in contention for a semi-final spot at the lucrative $3.65 million year-end finale.

Earlier in the day, Wimbledon champion Roger Federer crushed his Argentine bogeyman David Nalbandian, 6-3, 6-0 jumping to the top of the group standings with a 2-0 record.

Agassi and Nalbandian sit second with identical records and the winner of their match on Friday will advance to the last four along with Federer.

Ferrero slipped to 0-2 with one round-robin match to play and is out of the tournament.

OLDEST PLAYER

Playing in his first event since a semi-final loss to Ferrero at the U.S. Open, the 33-year-old Agassi looked every bit like the oldest player in the draw during a one-sided opening set.

Lacking the snap and resolve he displayed in his opening loss to Federer, Agassi watched and the sellout crowd sat silent as his shots sailed long, wide and into the net.

At the opposite end of the court, Ferrero was taking a page of out Agassi's playbook, pounding home two return winners to register a pair of breaks.

Unable to find his rhythm, Agassi's frustration came to an explosive head at 2-1 in the second with the Australian Open champion splintering his racket after angrily slamming it against his foot.

But the outburst seemed to spark Agassi into action as he slowly settled into the match.

With the latter part of his career marked by and spectacular comebacks and a single-minded self-belief, Agassi once again dug deep into his reserves on the floodlit court battling to stay in the contest until securing the crucial break to go up 5-3 in second.

He served out the set to even up the match.

Energised by the packed crowd, Agassi would seize control in the decider, breaking Ferrero to go 2-1 up and never allowed the Spaniard an opportunity to get back into the contest.

"It was like two different matches out there," Agassi said.

"I didn't have much of a rhythm in that first set and if you're second guessing against a guy like Ferrero he makes you pay the price."

Red Group play continues on Thursday with Roddick facing Rainer Schuettler and Carlos Moya battling Guillermo Coria.