(CNN) -- Defending champion Novak Djokovic has crashed out of the ATP World Tour Finals at London's O2 Arena, despite a 7-6 6-3 victory over Rafael Nadal on Friday.
The Serb went into the match knowing he needed to beat the out-of-sorts Spaniard -- and hope Nikolay Davydenko lost to Robin Soderling in the night match.
However, Russian Daydenko claimed a hard-fought three-set victory, meaning he went through to the semifinals as runner-up to Soderling, who topped the group.
This should have been a match to decide the winner of Group B but instead second seed Nadal went into the contest already out of contention for a last-four place while Djokovic knew his fate was not in his own hands.
Nadal won all but four of their first 18 meetings but Djokovic has had the upper hand recently, beating Nadal convincingly in their last two matches, including in Paris earlier this month.
Djokovic went on to win the title in Bercy, his fourth since the start of October, but that effort took its toll and he has looked weary and frustrated this week.
He began well, though, breaking Nadal in the opening game only to lose his serve straight away.
The third seed then made it three breaks in a row when Nadal served an untimely double fault.
The 23-year-old had a chance to level once again but this time Djokovic held firm. Nadal did retrieve the break in the eighth game, though, when Djokovic netted a backhand.
With no further openings, the set went to a tie-break, and it was the Serb who forged ahead, Nadal unable to cope with the flat hitting from the Djokovic racquet.
The 22-year-old had lost all five previous tie-breaks between the pair and he looked to have blown his chance to change that statistic when he slipped from 6-2 to 6-5 but he finally clinched it on his fourth set point when a Nadal forehand dropped just wide.
The Australian Open champion saved a break point in his opening game of the second set but it looked to have come at a cost, Nadal taking a medical time-out at the change of ends to receive treatment to his back.
After missing three months of the season with knee and abdominal injuries, another problem was the last thing he would have wanted, particularly with the Davis Cup final next weekend.
Djokovic, who was shortening the points very effectively as he looked to save what little energy he had left, duly broke in the next game to take a 3-1 lead.
That seemed certain to be more than enough, and he missed another chance to break at 4-1, but Nadal was not finished.
He saved two match points with Djokovic serving at 5-3, the first with a terrific backhand down the line, but he could not take a break point and the third seed sealed victory on his third match point.