Novak Djokovic kept alive his chances of reaching the semifinals of the ATP World Tour Finals, beating Rafael Nadal 7-6 (5), 6-3 Friday for the Spaniard's third straight loss.
Roger Federer, Juan Martin del Potro and Robin Soderling have clinched spots in the final four of the season-ending tournament.
Djokovic won for the second time in the round-robin phase. For the third-ranked Serb to advance, Soderling must beat Nikolay Davydenko in the late Group B match.
Nadal leaves the tournament without having won a set. He is on a four-match losing streak after losing to Djokovic in this month's Paris Masters semifinals. If Djokovic advances, he can overtake Nadal for the No. 2 ranking by winning the tournament.
Nadal finished with nearly three times as many unforced errors as winners — 35 to 12. He needed treatment on his lower back at 2-1 in the second set and was broken in the next game.
The second-ranked Spaniard saved two match points in the final game before sending a backhand wide on the third.
Djokovic had even more errors — 37 — but hit 21 winners and made fewer mistakes than Nadal when it mattered.
Nadal had broken back twice in the first set to reach the tiebreaker, where he shanked a couple of forehands and fell behind 6-2. He saved three set points before sending a forehand wide on the fourth.
The Spaniard showed flashes of his speed, chasing down a number of Djokovic's drop shots at the net. But his efforts were usually in vain, as most of his returns merely resulted in easy volley winners for the Serb.
Nadal's season has been interrupted by injuries. He is 1-9 against top-10 opponents since losing to top-ranked Federer in the Madrid Masters final in May.
In the other group, Federer and del Potro reached the semifinals Thursday while Andy Murray was eliminated. Fernando Verdasco of Spain, Nadal's teammate in next weekend's Davis Cup final against the Czech Republic, also went 0-3 in the round-robin phase.