LONDON: Rafael Nadal was beaten in straight sets by Robin Soderling in his opening match at the ATP World Tour Finals on Monday, the Swede repeating his shock French Open win over the Spaniard.

Soderling saw off Nadal 6-4, 6-4 inside an hour and 38 minutes at London's O2 Arena in their Group B match at the season-ending tournament of the world's top players.

Four-time French Open defending champion Nadal had had his 31-match winning streak there broken in May by Soderling, who in becoming the only man to beat Nadal at Roland Garros, went on to reach the final.

And the Swede repeated the upset with a tidy performance at the former Millennium Dome, at times giving the Australian Open champion the run-around on the medium-paced court.

"It was so nice. I was very nervous at the start but I got off to a great start," Soderling said.

"I managed to play really well on the important points and I really served well when I needed to.

"Winning against the world number two is not bad."

In-form Soderling, the world number nine, broke into the top 10 just over a month ago and was the first reserve for this tournament. He was called up after US Wimbledon finalist Andy Roddick withdrew due to a lingering knee injury.

The 25-year-old Monte Carlo resident has won only one tournament this year, the Bastad clay court title in his native Sweden.

Soderling took the first set within 40 minutes, breaking Nadal twice, including in the crucial final game when the Spaniard's unforced errors handed the Swede the set.

Nadal won the toss and chose to receive but the left-hander found himself 3-0 down within 10 minutes.

Soderling held serve then broke when Nadal sent a shot into the net. The Swede then won the next game to love, sealing it with an ace.

Nadal won his first game to pull it back to 3-1 then broke Soderling back when the Swede fired wide after a rally. The Mallorcan levelled the scores by taking the next game to love, finishing with an ace.

After Soderling held serve, two consecutive line call challenges saw the serving Nadal 0-30 down but he recovered to take the game.

The Swede won the next game to love, leaving Nadal needing to hold serve to stay in the set. Soderling took him to deuce, gained the advantage when Nadal hit the net and took the set when his opponent fired long.

Soderling held serve in the first game of the second set but Nadal held serve to love and broke the Swede with a rare foray to the net to finish a rally.

However, Soderling was in fighting spirit and took a 0-40 lead next game, winning it by challenging a baseline call.

The fifth game went to seven deuces, with Soderling finally converting an advantage at the sixth attempt.

The next three games went with serve to make it 4-4. Soderling then fought off a deuce to leave Nadal serving to stay in the match.

Soderling took the Spaniard to deuce and gained a first match point when Nadal hit a shot narrowly wide. But Soderling shot just long to take it back to deuce.

The Swede went to match point again with a cross-court shot and won the contest when Nadal fired long.

Serbia's defending champion Novak Djokovic and Russia's Nikolay Davydenko are also in Group B, from which two go through to the semi-finals.