Djokovic, who was broken in the first game but managed to break back in the tenth game, edged the first set on a tie-break but lost seven games in a row as the fourth-seeded Russian roared back to level.

The third set was a tense affair but Djokovic held his nerve to triumph.

Davydenko or Juan Martin del Potro will join him in the last four after the Argentine beat Jo-Wilfried Tsonga in yesterday's other Gold Group match.

The top two will go through to the semi-finals, along with two from the Red Group of Roger Federer, Andy Murray, Andy Roddick and Gilles Simon.

Tsonga is definitely out after his second defeat of the tournament, so the winner of Thursday's clash between Davydenko and Del Potro will progress.

Del Potro kept alive his chance of qualifying for the semifinals with a straight-sets win over Tsonga.

The seventh seed wrapped up a vital 7-6(4), 7-6(5) win after both men had lost their opening games in the Gold Group.

Del Potro edged a tight first set and held off a Tsonga fightback in the second before winning the battle of the Masters Cup debutants.

The Frenchman fired 17 aces throughout the match but also committed 38 unforced errors which cost him dear at crucial moments, and Del Potro, with four aces and 18 unforced errors for the match, played a more consistent game and gained himself the victory in two close sets.

Tsonga was broken in the very first game but continued to go for his shots and he broke back to level at 2-2 with a rasping cross-court forehand.

From then on the first set went with serve and into a tie-break, where Tsonga's errors proved far more costly.

Del Potro clinched the set with a big serve of his own and started the second set in confident fashion, breaking to lead 2-0.

Tsonga quickly fought back again to level and also kept his hopes alive when he trailed 15-30 at 4-5 with a slam-dunk smash and equally athletic volley that helped him hold.

The Frenchman's impressive performance was captivating, and the atmosphere reached fever pitch as the entranced crowd burst into applause.

But Del Potro again seized control of the second-set tie-break with a run of four straight points, capped by a rasping forehand winner on the run, and he sealed his victory with an overhead.