INQUIRER Sports

LONDON- Novak Djokovic kept alive his hopes of reaching the last four of the ATP World Tour Finals as the defending champion defeated Rafael Nadal 7-6 (7/5), 6-3 on Friday.

With Sweden's Robin Soderling already through from Group B and Nadal out after successive defeats, Djokovic is competing with Nikolay Davydenko for the last semi-final spot at the prestigious season finale.

Djokovic already knew his fate was out of his hands as even this victory over Nadal won't be enough to qualify him if Davydenko beats Soderling later on Friday at London's O2 Arena.

The Serb at least did all he could to make it. Djokovic's gutsy display was aided by a back injury suffered by Nadal early in the second set that left the Spaniard operating well below 100 percent.

Djokovic faces a wait of several hours to learn if he has qualified and he said: "I will try to use the same procedure I do before each match. I will behave now as I'm playing on Saturday.

"And if I don't, as I said, it's absolutely deserved for Davydenko if he qualifies. He played really well. There's nothing to do there. I just have to wait and see."

Nadal, who failed to win a set in his three matches, admitted he went into the tournament with low expectations.

"It's disappointing to go out if you arrive here with the feeling that you have a big chance to win but I didn't arrive here with that feeling," he said.

"I know before that the tournament was going to be really tough. But every day I tried my best. Nobody can say otherwise.

"And I think I improved a little bit. But I'm playing against the best players of the world. It wasn't enough on this surface."

In Wednesday's defeat to Soderling, world number three Djokovic looked like he was running on empty and he had conceded a grueling year was taking its toll.

Nadal hardly looked much more energized in defeats to Soderling and Davydenko, although the world number two also has next month's Davis Cup final against Czech Republic on his mind.

Djokovic broke in the opening game when Nadal tamely netted a forehand, but the Serb immediately dropped his own serve. He didn't have to wait long to be gifted the lead again though as Nadal double-faulted on break point in the next game.

After that error-strewn start, there was a slight improvement from both men. Although Nadal was never anywhere near his best, he broke back at 3-4 down and that was enough to send the set to a tie-break.

Djokovic summoned up enough willpower to seize the initiative in the breaker as he moved 6-2 ahead. Nadal saved three of those set points but the Spaniard then sent a forehand wide to surrender the set.

Nadal needed a lengthy spell of treatment on his lower back after the third game of the second set and looked in some discomfort while the doctor massaged the problem area.

He decided to play on despite the pain but immediately dropped his serve to put Djokovic within sight of victory.

Nadal saved two match points and then earned a break point as a clearly drained Djokovic tried to limp over the finish line.

He finally did just that, saving the break point and serving out before celebrating by manically playing his racquet as though it was a guitar.

Also qualified for the semi-finals are Juan Martin del Potro of Argentina and Swiss world number one Roger Federer.