AFP
 
Shanghai, Nov 12: World number three Novak Djokovic survived a big scare against Nikolay Davydenko to reach the Masters Cup semi-finals on Tuesday. 

A day after four-time champion Roger Federer slumped to Gilles Simon, the Australian Open champion won the first set but fell apart in the second before rallying to win 7-6 (7/3), 0-6, 7-5.

The result means Djokovic tops Gold Group and eliminates Jo-Wilfried Tsonga, who was beaten by Juan Martin del Potro earlier.

"I did expect a tough match against Nikolay," said the Serb. "I had some very unexplainable ups and downs in that second set and it was very hard to come back."

Djokovic recovered from an early break to dominate the first-set tie-break, setting up three match points with a pair of screaming aces and taking the lead when Davydenko double-faulted.

A convincing win looked on the cards but Djokovic followed Federer by imploding in the second set, ranting and hurling his racquet as he dished up a series of unforced errors including a wide forehand to level the match.

But Djokovic survived early break points in the third and his composure grew as he walloped a forehand and Davydenko misfired for the crucial break 6-5. Another big forehand was enough to seal the match.

Djokovic lost all three group matches on debut last year, while Davydenko has qualified for the season finale four times and reached the semi-finals in 2005.

The two had never completed a match together after the Serb withdrew from their Davis Cup meeting in February complaining of dizziness and exhaustion.

Earlier del Potro won a tense encounter with French livewire Tsonga 7-6 (7/4), 7-6 (7/5) to breathe life into his campaign after his opening loss to Djokovic.

The 20-year-old Argentine showed steely determination as he won two gripping tie-breaks to revive his semi-final hopes.

"The first match I was a little nervous. I was playing the world number three and it's difficult to play against Novak," del Potro said.

"Against Tsonga it's completely different. He served much better, but he's not too consistent. He made more errors. So that was good for me."

Tsonga, who won this month's Paris Masters, is out after losing both his opening matches.

The Muhammad Ali-lookalike thundered 12 aces in the first set but paid for 21 unforced errors as he went down 7-4 in the tie-break.

Two points from defeat at 4-5, the pumped-up Tsonga recovered spectacularly with a double jumping overhead and swatted forehand volley to stay in the match.

Del Potro took control of the second-set tie-break with a glorious backhand pass and Tsonga netted on the third match point.

The elite, 4.45-million-dollar Masters Cup features an eight-man field who each play three group matches before the semi-finals.