Shanghai - Novak Djokovic broke his duck at the Masters Cup, winning his first career match at the season wrap-up after three 2007 losses.

The Serb overpowered Argentine Juan Del Potro 7-5, 6-3 to take the early lead in the Gold group.

"I'm happy to win, that's for sure, I'm satisfied," said Australian Open champion Dokovic.

"I played really well from the start and felt good on the court. But then suddenly I just lost momentum and started serving really badly.

"He got back to the game. It was my fault, but I played well in the important moments. I'm happy to get through in straight sets."

Frenchman Jo-Wilfried Tsonga was making his debut at the year-end classic after clinching the last place in the eight-man field a week ago by winning the Paris title.

Tsonga, who lost the Australian Open final to Djokovic 11 months ago, was facing Russian Nikolay Davydenko.

Djokovic struck eight aces in a victory which lasted just shy of two hours, with Del Potro saving seven of the 11 break points he faced.

The 21-year-old Serbian winner improved to 2-0 over the Argentine, who has been nursing a painful split toenail for several months and still has Shanghai and the Davis Cup final to complete before he can have the injury taken care of.

"I feel a little pain, but is always like this since the US Open," said the 20-year-old. "I can play, I can run, but is difficult sometimes.

"I have two more matches. I want to do my best, and then we will see what happens with my toe."

Djokovic now stands 2-0 in the series after defeating the South American in the 2007 US Open third round.

"When you play against Nadal, Federer, or Djokovic, you have just one or two chances in the match," said debutant Del Potro. "If you don't take them - you lose.

"That's what happened today. I played a great first set, I had breakpoints. I didn't get them. He began to play much better than me. That was the key." (dpa)