If either of his rivals win later in straight sets, Nadal qualifies for the final four. Should it go to three sets, the world number two form Mallorca could still likely squeeze into the weekend on ratio of games won and lost between the contending trio.
The rival Red group will be decided on Friday, with Roger Federer struggling for the first time to assure himself a semi-final spot at the year-end event he's won three times.
The Swiss faces a Friday must-win scenario with Andy Roddick, whom he's beaten on 14 or 15 occasions.
Djokovic made a breakthrough this season with semi-finals at Roland Garros and Wimbledon, five ATP titles including Master Series honours in Miami and Montreal.
But the 20-year-old's result have tailed off in the last two months, with Djokovic losing a Madrid semi-final and going down in the first round at Paris Bercy.
The Serb later revealed that he had wisdom teeth removed, partially accounting for his poor form.
But Djokovic flew East last week complaining of the fatigue from Shanghai (dpa) - Rafael Nadal put sagging Serb Novak Djokovic out his his 2007 late-season misery with a 6-4, 6-4 victory in a final Gold Group clash at the Masters Cup on Thursday.a long and arduous season. He leaves China with three group defeats and the chance to re-group for 2008.
Nadal improved his record in the series to 6-2, winning four of their last five meetings this season.
The Spaniard, who qualified the last three years for Shanghai, took the first set in 45 minutes after Djokovic saved a set point.
But the Serb showed late-match fight in a stirring effort in the high-tension eighth game, which Nadal had to struggle to hold, 5-3 before taking victory two games later with a backhand down the line.
Djokovic fired nine aces while losing serve three times. Nadal has been pacing himself at the end of the season after struggling with tendinitis in both knees since late summer.
But the three-time Roland Garros winner has shown no sign of problems this week in China as he winds up his season