(CNN) -- U.S. Open champion Juan Martin del Potro kept alive his challenge at the ATP World Tour Finals in London with a nervy 6-4 3-6 7-6 victory over Fernando Verdasco on Tuesday.
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 semifinal place.
And the 21-year-old rose to the challenge, despite a second set wobble, to give him a chance of reaching the last four, providing he beats Roger Federer in his final match on Thursday.
Verdasco, 26, is appearing in the Tour Finals for the first time after enjoying the best season of his career -- but the Spaniard no looks certain to make an early exit after his second defeat of the round robin stage.
Both players had lost their opening matches. Del Potro had been unable to subdue Murray in a three-set encounter on Sunday, while Verdasco dominated the opening stages against Federer but also ended up losing in three sets.
Del Potro quickly found his range with some thudding ground-strokes and broke in the third game for a 2-1 lead.
The Argentine 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 could not convert though and del Potro took the set.
But, 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. Del Potro broke in the sixth game when he successfully challenged that Verdasco's forehand was out.
But Verdasco was not going to surrender just yet. He saved a match point at 2-5 and then broke back as del Potro served for the match.
Del Potro was unable to finish off another match point in the 10th game. But the Argentine finally completed a hard-fought win in comprehensive fashion as he blew Verdasco away 7-1 in the tie-break.