London  - Roger Federer and Andy Murray kick-started the ATP World Tour Finals Sunday after a move from China to Britain, with both earning opening group victories at the eight-man year-end showcase.

Top seed Federer lost the first set of his career to Fernando Verdasco, but regrouped after a big effort to defeat the Spaniard 4-6, 7-5, 6-1 in their Group A clash of an event held for the last four years in Shanghai.

Murray lit up the 17,500-strong audience in the darkened hall deep in the far precincts of East London with his opening-day win over Argentine Juan Del Potro 6-3, 3-6, 6-2.

Murray and the US Open champion - whose form has dived since the day two months ago when he beat Federer in the final - were the first pair to taste the atmosphere of the new venue.

"It's different, you can't see the crowd when you're on the court it's so dark - but you obviously hear them," said Murray.

"It was a great atmosphere. It's not as much interaction with the crowd. But the atmosphere was excellent."

Federer, who can end the season again on number one if he wins all three of his group matches to hold off chasing rival Rafael Nadal, had his troubles with Spain's Verdasco, coached by a brain trust which also includes Australian Darren Cahill, who turned down a chance to coach the Swiss several seasons ago.

But after dropping the first set after starting with a 3-0 record and six sets won against Verdasco, Federer broke in the final game of the second set as the Spanish armour began to crack.

The top seed and 15-time Grand Slam champion took a 3-0 lead in the final set, ending his fighting victory after just on two hours.

Monday's programme will be a huge psychological test for second seed Nadal as the Spaniard takes on the only man to have ever beaten him at Roland Garros, Sweden's Robin Soderling.

Form player Novak Djokovic of Serbia, winner of three titles in six weeks, plays Russian Nikolay Davydenko as the last of the eight elite take to the court for the final competition of a long season with 1.6 million dollars on the line for an undefeated champion to be crowned next Sunday.

Murray took two hours, ten minutes to secure the opening-day success, with Del Potro unable to overcome a finishing burst from the world number four.

"It was a really good start," said the winner. "Me and Juan haven't played that much since the US Open. I kind of expected a little bit of a scrappy match."

Murray, with an ATP-leading six titles in 2009, secured victory with 30 winners plus early and late breaks in the final set.

His Argentine opponent was undone by 38 unforced errors. Murray converted on five of a dozen break point chances, racing away to a 5- 0 lead in the opening set and winning it on his seventh set point.

In the third, Del Potro's fifth double-fault handed Murray a pair of match points and he converted on the first, a backhand winner.

"I'm obviously happy I managed to come back in the third, because he was playing well," said Murray.

Both players were appearing in the year-end finale for the second straight season, with Murray's record in the series improving to 5-1 after their fourth meeting of 2009.

Del Potro, never the same since winning his US Open crown, suffered with a nosebleed after three games and never showed his top form.

"Andy started to play very hard, very good. He broke my serve very early, then he took the control of the first set.

"He played great tennis in the third set. He was a little lucky, but you need the luck to win. And today (it) was with him." (dpa)