Serbian world number three Novak Djokovic [Images] survived a second-set implosion to beat Russian Nikolay Davydenko 7-6, 0-6, 7-5 on Tuesday and become the first player into the semi-finals of the Masters Cup.

The 21-year-old, who lost all three of his matches on his Masters Cup debut last year but won his opener against Juan Martin Del Potro on Sunday, is guaranteed to top Gold Group after prevailing in a two-hour, 18-minute encounter.

Argentine Del Potro beat Jo-Wilfried Tsonga 7-6, 7-6 in the other group match to keep alive his hopes of reaching the knockout stage and end those of the Frenchman.

Davydenko, who beat Tsonga in his Sunday opener, will now have to beat Del Potro in a winner-takes-all encounter on Thursday to reach the Masters Cup semi-finals for a second time.

The 27-year-old Russian was at his dogged best at the start of Tuesday's match and broke the second-seeded Australian Open [Images] champion on his first service game.

Djokovic held his nerve, however, broke back when the world number five was serving for the set and raced to a 4-0 lead in the tiebreak that followed.

A couple of aces gave him set point, which the Russian fourth seed conceded with a double fault.

The young Serbian fell apart in the second set, smashing his racket about and clearly seething when a line call and subsequent challenge went against him.

Davydenko, a seasoned campaigner playing in his fourth Masters Cup, seized his chance to even up the match in 26 minutes and grabbed two break points in Djokovic's first service game of the deciding set.

Djokovic, though, regained his composure and battled back to save his serve. The match looked destined for another tiebreak when he broke for 6-5 and served out for victory.

Seventh seed Del Potro broke Tsonga's first service game and, although the Frenchman broke back, always looked the more likely to win a tight contest.

"I know his game," said the 20-year-old Del Potro. "I know what can I do against this player, and that's what I did today. I played very good."

Sixth seed Tsonga served up 17 aces and rattled home 42 winners but that good work was undone by 38 unforced errors, the last of which came when he put the ball in the net to end the second tiebreak.

"I lost with two tiebreaks," said the 23-year-old Frenchman, runner-up to Djokovic at this year's Australian Open. "I know he played better than me in the tiebreak. I missed some easy balls and that's it."

• Complete tennis coverage
• All you want to know about Sania Mirza