It took a while, but Rafael Nadal finally showed up at the ATP's end-of-year fiesta on Monday when he lit up the second day of the World Tour Finals with a compelling round robin victory against Andy Roddick.

Former Argentine soccer great Diego Maradona's presence in Novak Djokovic's entourage during the Serb's easy win over Tomas Berdych had provided the day's biggest talking point until world number one Nadal slugged out a 3-6, 7-6, 6-4 victory.

The Spaniard found London's iconic O2 Arena an unhappy hunting ground last year when he suffered three demoralising defeats but on Monday, dressed in vivid pink, he recovered from a shaky start to show why he is the game's dominant force.

After three one-sided contests so far, the elite eight-man tournament boasting a $1.6 million jackpot needed a match to quicken the pulse and Nadal and Roddick provided it on cue.

Roddick briefly slipped out of the world's top-10 this year but the 28-year-old American, a huge favourite in London for his three Wimbledon finals against Roger Federer, demonstrated the qualities that make him such a dangerous adversary.

He fired 17 aces past Nadal, three 140mph (225kph) bullets coming in succession in the third game, but it was the quality of his baseline play that threatened to continue his opponent's torrid time at the venue beside the River Thames.

Only when Nadal claimed the second set on a tiebreak after trailing by a set and a break did Roddick run out of ammunition.

Nadal carved out a crucial break in the fifth game of the decider, pouncing on a tired Roddick volley before clinching victory in two hours 33 minutes to the delight of the Spanish fans sprinkled around the cavernous 17,500-capacity venue.

"I was a little bit lucky tonight," Nadal, who missed last week's Paris Masters with a shoulder problem and had not played a competitive match since October, told reporters.

"I started the match a little bit nervous. Five weeks without playing and on a tough surface for me it was always going to be difficult against one of the best servers in the world. I think I was very close to lose today," he added.

Roddick was making his O2 debut after injury reduced him to a spectator here last year and he was just four solid service games away from a notable victory when he broke Nadal's serve to lead 2-1 in the second set.

However, the tide began to turn against him when he surrendered his serve in the next game and from that point on he was never able to dominate the bullish Spaniard again.

"The difference was he found his range on his forehand in the second and third sets," Roddick said.

"He was able to find his defensive forehand more and wasn't spraying it. That changed the dimension of the rallies a bit," he added.

Holders of night session tickets clearly got the better deal on Monday, even if Maradona's afternoon appearance in Djokovic's corner trumped the evening visit of pop star Kylie Minogue.

The former World Cup winner is a big fan of Djokovic's game and he would have been impressed with what he witnessed as razor-sharp Serb outclassed a disappointing Berdych 6-3, 6-3.

Afterwards Djokovic joked that Maradona, out of work since losing his job as Argentina coach, could offer him some tips on "high shots", a cheeky reference to the infamous "Hand of God" goal that knocked England out of the 1986 World Cup.

"It's a great honour having you around. When he came in during the middle of the first set, I wondered whether I should play with my legs or my hands!" Djokovic said.

Thankfully he stuck to his tennis skills and they proved far too good for Berdych. Nadal, however, will be an altogether tougher proposition on Wednesday.

Aiming to grab that elusive World Tour Finals title, Mahesh Bhupathi and Max Mirnyi began their campaign on a right note with a win but Leander Paes and Lukas Dlouhy's chances suffered a setback due to defeat in the opening group match.

Bhupathi and Mirnyi, seeded fourth, scored a hard-earned 7-6(2), 6-4 win over Lukasz Kubot and Oliver Marach in their opening clash in Group B.

Paes and Dlouhy, seeded third, though went down fighting 3-6, 6-7(3) against Mariusz Fyrstenberg and Marcin Matkowski.

Paes and his Czech partner will have to win the remaining two matches as only the top two teams from each group will advance to the semi-finals.

They will take on Jurgen Melzer of Austria and Germany's Philipp Petzschner in their next match.