Djokovic kept alive his hopes of reaching the semifinals but he will have to wait until Nikolay Davydenko takes on already qualified Swede Robin Soderling in the final round-robin match of the season-ending event at the O2 Arena before knowing if his two Group B victories will be enough.
Nadal once again looked a shadow of the player that began the year in such devastating fashion. He lost his opening two services games although his instinctive battling qualities allowed him to break a weary-looking Djokovic twice to take the opening set into a tiebreak. Some weak baseline errors allowed Djokovic to forge into a 6-2 lead before Nadal won the next three points.
He dropped his serve again in the second set with yet another forehand error and Djokovic stayed out in front to claim victory. On Thursday, world number one Roger Federer squeezed into the semifinals despite a 6-2, 6-7, 6-3 defeat by Juan Martin del Potro but Briton Andy Murray literally missed out by a fraction.
The final round-robin action in Group A had players, tournament organisers and journalists scratching their heads as all three contenders ended with virtually identical records.
Murray's victory over Spain's Fernando Verdasco meant any win for Federer later would have sent the Scot through but Federer suffered badly again at the hands of the giant south American.
Federer, Del Potro and Murray all posted two wins and a 5-4 sets win/loss ratio meaning that calculators were as useful as tennis rackets to work out which two players would progress to Saturday's semi-finals by virtue of a better game percentage.
A bemused-looking Del Potro edged home favourite Murray by one game.
Paes-Dlouhy lose
Leander Paes and his partner Lukas Dlouhy rounded off their disappointing campaign with their third successive defeat.
The Indo-Czech pair lost their last Group B match 6-7 (7-1), 4-6 to Max Mirnyi and Andy Ram
