US Open champion Juan Martin del Potro kept alive his challenge at the ATP World Tour Finals with a 6-4, 3-6 7-6 victory over Fernando Verdasco yesterday.

After losing his opening Group A match to Andy Murray, Del Potro knew he had to see off Verdasco in their first ever Tour meeting to remain in contention for a semi-final place.

The 21-year-old rose to the challenge with a typically belligerent display of guts and power-hitting and could qualify for the last four with a win in his last match, against Roger Federer, tomorrow.

Verdasco, 26, is appearing in the Tour Finals for the first time after enjoying the best season of his career. But the left hander looks certain to make an early exit after his second defeat of the round robin stage.

Del Potro said: "I served much better than my other match. I was very focused in the important moments, especially in the tiebreak and I took my opportunities.

"Of course, I felt nervous because if I lose, I go home. But it's an important victory for my confidence."

The towering Argentine showed the form that lead him to victory in the US Open as he took control of the first set.

He quickly found his range with some thudding ground-strokes and broke in the third game for a 2-1 lead.

Del Potro remained in control until he had to serve for the set at 5-4, then he faltered and allowed Verdasco two break points. The Spaniard couldn't convert though and Del Potro took the set.

Hitting with increasing accuracy from the baseline, Verdasco began to wear down Del Potro and broke in the eighth game for a 5-3 lead before serving out the second set.

The final set went down to the wire as both players fought for their tournament lives. But the Argentine finally completed a hard-fought win in comprehensive fashion as he blew Verdasco away in the tie-break.

Djokovic prevails

Defending champion Novak Djokovic handed Nikolay Davydenko another painful defeat at the ATP World Tour Finals as the Serb secured a 3-6 6-4 7-5 victory on Monday.

Djokovic beat Davydenko to win the final of this prestigious end-of-year event 12 months ago and the world number three came from behind to frustrate him again in his opening Group B match at London's O2 Arena.

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