Robin Soderling repeated his French Open heroics with a 6-4 6-4 victory over Rafael Nadal at the Barclays ATP World Tour Finals in London.

Soderling became the first man to beat the four-time champion at Roland Garros in the spring and with this result he could have scuppered Nadal's chances of overtaking Roger Federer to become the year-end world number one.

The Swede went on to reach the final in Paris and has since climbed into the world's top 10, and he showed he could be a contender for the prestigious end-of-season crown at the O2 Arena with a display of power and nerve in the Group B opener.

Soderling's victory over Nadal at Roland Garros was arguably the most surprising result of the season, the Swede having lost his three previous matches to the world number two.

There is no love lost between the pair and Nadal would have been desperate to avenge that painful defeat but things began badly as the second seed dropped his opening service game.

The fast indoor surface was always likely to suit Soderling - a late replacement for the injured Andy Roddick - more than Nadal, and he peppered the lines in the opening stages.

The Spaniard is a natural-born fighter, though, and a more aggressive approach did the trick as he broke back for 2-3, but that did not shake Soderling's belief and a netted Nadal forehand gave the 25-year-old a set point on his opponent's serve - which he took thanks to an uncharacteristic unforced error from the Australian Open champion.

Soderling's huge serve was the bedrock of his first-set success but it cost him in the third game of the second as two double faults paved the way for Nadal to forge ahead. However, the Swede simply upped the power level and forced three break-back points - taking the final one courtesy of a successful Hawk-Eye challenge.

A titanic fifth game finally went the way of Soderling and, although there were flashes of Nadal brilliance - notably some stunning passing shots - they were too infrequent to really put the underdog in trouble. And the increasingly-frustrated Majorcan found himself staring down the barrel in the 10th game - but this time a break point for Soderling was match point.

Nadal saved one but the second chance was gleefully gobbled up by the Swede courtesy of a wayward Nadal backhand.