Novak Djokovic on his way to victory (AP)

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Talek Harris

Shanghai - World number three Novak Djokovic saw off a spirited challenge from Argentina's Juan Martin del Potro in a gripping start to the Masters Cup on Sunday.

Djokovic prevailed in a tight first set and earned a crucial break late in the second to take it 7-5 6-3 for his maiden win in the season finale after losing all three round-robin matches last year.

"Last year I didn't have a lot of success. I lost every single match I played, but this time it’s different," Djokovic said.

Sporting a flashy black and gold outfit to match the glitzy occasion, the Australian Open champion soon had the measure of Del Potro's big serve and whipped a forehand on his third breakpoint for a 3-1 lead in the first.

The Serb was starting to enjoy himself and he consolidated at 4-1, helped by a fabulous backhand drop that landed just inside the line and spun out at a right angle.

Painful toe

The 1.93m Del Potro hit back with a break at 5-3 but slammed his racquet to the ground in frustration as he gave up a break point and the set by netting after a long rally at 5-6.

Del Potro, 20, who has been playing with a painful toe injury since the US Open, produced two memorable backhand passes to go a break up in the second but was broken back immediately as he twice netted on the same wing.

Djokovic sprayed two backhands of his own and then looped a forehand past the advancing del Potro to break for 5-3, converting the first match point as his opponent netted.

Del Potro said: "When you play against Nadal, Federer or Djokovic, you have just one or two chances in the match.

"If you're not focused enough to take it, you lose, and that's what happened."

Russia's Nikolay Davydenko was playing French livewire Jo-Wilfried Tsonga in Sunday's later Gold Group match, while top seed Roger Federer opens his bid for a third consecutive title on Monday.

World number one Rafael Nadal is skipping the tournament, citing fatigue and tendinitis.