Juan Martin Del Potro clinched his first victory in Group A of the World Tour Finals as he overcame Fernando Verdasco 6-4 3-6 7-6(1) at the O2 Arena.

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The Argentine edged out his opponent with a clinical and efficient display in the opening set, but Verdasco hit straight back with an inspired array of groundstrokes to force a deciding third set which went to a tie-break.

The match continued to be fiercely contested with both players trading blows from the back of the court, but the US Open champion found the extra invention to outwit his opponent and claim an important win in London.

Both Del Potro and Verdasco went into the match having lost their opening encounters, against Andy Murray and Roger Federer respectively, and needed to get their campaigns back on track.

The Argentine settled quickly with a service hold of real conviction before he broke Verdasco to seize the early initiative as his opponent was pushed into two unforced errors from 15-30.

Del Potro continued to serve with assurance and, despite being forced to save two break points, held on to close out the set from 5-4 with an obdurate hold and stamp his authority on the match.

The start of the second set saw both players holding serve relatively comfortably with neither able to put the other under too much pressure.

But it was the Argentine who applied the most, and Verdasco had to find two huge serves and a rasping backhand winner down the line to remain stubbornly ahead at 4-3.

The Spaniard's momentum continued unabated as, despite being pegged back to 30-30 after winning the opening two points, he forced Del Potro to over-hit two forehands which enabled him to force a decisive break.

The start of the third set was a masterclass of shot-making from both players as ferocious ground-strokes were exchanged with crunching winners that peppered the lines.

But Del Potro again stepped up his intensity while leading 3-2 and carved out two break points at 15-40 with an outrageous backhand winner, before he successfully challenged a backhand from the Spaniard to seal the break.

The pressure was on the Argentine, whose only completed win since Flushing Meadows was against the now retired Marat Safin, and the tension began to creep into his game.

Verdasco broke in stunning fashion at 5-3 to haul himself back into the match as Del Potro lost his composure and fired two forehands long to squander his advantage.

Verdasco again showed immense courage as he survived another break point, and the Spaniard levelled the set at 5-5 courtesy of two fierce forehands.

Del Potro was the fastest to settle in the tie-break as he snatched the first mini-break with a crisp forehand.

Verdasco buckled under the relentless pressure as the Argentine closed out victory in an emphatic fashion which belied the contest which had preceded it.