LONDON: There are plenty of special effects inside the O2 Arena for the ATP Tour Finals but nothing could match the sight of Roger Federer in full flow as he beat Andy Murray on Tuesday to guarantee the year-end No.1 ranking.

Roger Federer of Switzerland reacts after winning his ATP World Tour Finals tennis match against Andy Murray of Britain in London November 24, 2009. [Agencies]

Federer did not have to be at his magical best but after a wobbly start he took control midway through the match and treated the 17,500 capacity crowd to some shots that only he can play, reeling off the last six games for a 3-6 6-3 6-1 victory.

His second three-set win in Group A meant that world number two Rafael Nadal can no longer close the points gap in the rankings and Federer will have the honour of finishing the year as the world number one for the fifth time in his career.

Only Pete Sampras, who managed the feat six times in the 1990s, and Jimmy Connors, who did it five times in the 70s, have achieved that since rankings were introduced in 1973.

"After having a rough 2008, coming back this year and being able to dominate and play at the top when the depth in tennis is so great at the moment, I think it's a wonderful achievement," Federer, whose year began in a shattering defeat by Nadal in the Australian Open final, told reporters.

"It's official. It's a wonderful feeling. I think this is more the night to celebrate number one than celebrate the victory over Andy really."

While Federer is untouchable in the rankings, the intricacies of tournament's unique format mean that his place in the semi-finals here is not yet guaranteed as Juan Martin del Potro's earlier victory over Fernando Verdasco meant that all four players in Group A can still progress.

Federer tops the table with two wins but defeat by Del Potro, the man who stopped him in his tracks in the US Open final, on Thursday and victory for Murray against Verdasco would mean calculators are needed to work out the final standings.

Towering Argentine Del Potro found his range to beat Verdasco 6-4 3-6 7-6 in the day session to make up for his defeat by Murray on Sunday, meaning that five of the six singles matches played here so far have gone the distance.

"I felt nervous because if I lost, I go home," the 21-year-old Del Potro, who hopes to have Argentina striker Carlos Tevez watching against Federer, told reporters.

"It was important, the victory today, to get confidence. I hope to play my best tennis against Roger."

There was a huge sense of expectation as Murray and Federer took the spotlight in the evening session for their 10th career meeting, six of which had been won by Murray, including a sensational scrap 12 months ago in Shanghai, the former host city for the tournament.

Federer broke Murray's serve in the opening game but the Scot hit back immediately to raise the noise levels in the darkened arena that has proved a spectacular backdrop for the world's top eight players to strut their stuff.

Federer played a poor game to drop serve in the sixth game and Murray consolidated the break with a slam-dunk smash that would not have looked out of place when the Chicago Bulls played an NBA game against Utah Jazz at the O2 last month.

When Murray claimed the first set, T-shirts were fired into the crowd by organisers but the party turned flat for Murray's fans from then on as he faded badly.

"I served so poorly that anyone would have looked good against me tonight," world number four Murray told reporters.

Bad news indeed when the man on the other side of the net happens to be Federer and the Swiss needed no second invitation to swarm all over an opponent who has caused him plenty of headaches in their previous career meetings.

Federer was clearly in a hurry to get the job done and pulled out all the stops in the third set, one crosscourt forehand played from almost in the first row of seats worth the entrance money alone.

On Wednesday Rafael Nadal faces Nikolay Davydenko needing a win to stay in the hunt for a semi-final place while world number three Novak Djokovic and Robin Soderling also square up.