MASTERS CUP, Shanghai: Dates: 9-16 November Starts: 0600/1000 GMT daily Coverage: Live on Sky Sports; live text commentaries on BBC Sport website; every match live on Radio 5 Live sports extra
Djokovic won despite suffering a slump in form in the second set
Novak Djokovic became the first player to book his place in the semi-finals of the Masters Cup with a tight 7-6 (7-3) 0-6 7-5 win over Nikolay Davydenko.
Djokovic edged the first set on a tie-break but lost seven games in a row as the 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 Tuesday's other Gold Group match.
Del Potro needed two tie-breaks to edge past Tsonga, eventually clinching a 7-6 (7-4) 7-6 (7-5) win.
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.
Davydenko certainly had enough chances to see off Djokovic but it was the Serbian who eventually prevailed.
After Djokovic was broken in the first game of the match, Davydenko served for the first set at 5-4 but the second seed fought back to level.
Two aces by Djokovic and two double-faults by Davydenko helped to decide the first set tie-break only for the match to be turned on its head completely in the second set as Djokovic crumbled.
He had to wait 41 minutes to win another game before pulling himself together to level at 1-1 in the decider.
The third set saw both players make mistakes but it was Djokovic who snatched victory - breaking Davydenko at 5-5 and serving out for a dramatic win.
"I did expect a close match," Djokovic said afterwards. "I had some unexplainable ups and downs, especially in the second set. I was also lucky to save several break points."
Tsonga's match with Del Potro was just as entertaining, with the Frenchman attacking throughout and using his huge serve to hit a succession of aces.
But mistakes at crucial times cost him dear and Del Potro's more consistent play brought him victory in two close sets.
"I played the important points very well in the second set, and that was the key to beating him," said Del Potro, who has been suffering from an injured toe.
He played better than me in the tie-breaks - I missed some easy balls and that's it
"He's not too consistent. He made more errors."
Tsonga's maiden appearance at the end of season championships has ended in disappointment and he cannot progress even if he beats Djokovic in his final match.
"I know he played better than me in the tie-breaks," said Tsonga. "I missed some easy balls, and that's it."