AFP

Shanghai, Nov 10: World number three Novak Djokovic and Russia's Nikolay Davydenko scrapped to hard-fought wins as the elite Tennis Masters Cup got off to a pulsating start on Sunday.

Djokovic saw off a spirited challenge from Argentina's Juan Martin del Potro 7-5, 6-3 before Davydenko came from a set down to edge Jo-Wilfried Tsonga 6-7 (6/8), 6-4, 7-6 (7/0) in the Gold Group's opening round-robin matches.

Top seed Roger Federer starts his bid for a third consecutive victory at the ATP season finale on Monday despite doubts over a back strain that forced him out of last week's Paris Masters.

The $4.45-million showpiece is already missing world number one Rafael Nadal, who pulled out citing fatigue and knee tendinitis.

In Sunday's opener, Djokovic prevailed in a tight first set and earned a crucial break late in the second for his maiden Masters Cup win after losing all three group matches last year.

"Last year I didn't have a lot of success. I lost every single match I played, but this time is different," Djokovic said.

Sporting a flashy black and gold outfit to match the glitzy occasion, the Australian Open champion soon had the measure of del Potro's big serve and whipped a forehand on his third break point for a 3-1 lead in the first.

The Serb was starting to enjoy himself and he consolidated at 4-1, helped by a fabulous backhand drop that landed just inside the line and spun out at a right angle.

The six-foot-six (1.93-metre) del Potro hit back with a break at 5-3 but slammed his racquet to the ground in frustration as he gave up a break point and the set by netting after a long rally at 5-6.

Del Potro, 20, who has been playing with a painful toe injury since the US Open, produced two memorable backhand passes to go a break up in the second but was broken back immediately as he twice netted on the same wing.

Djokovic sprayed two backhands of his own and then looped a forehand past the advancing del Potro to break for 5-3, converting the first match point as his opponent netted.

"When you play against Nadal, Federer or Djokovic, you have just one or two chances in the match," del Potro said. "If you're not focused enough to take it, you lose, and that's what happened today."

In the later match, Paris Masters champion Tsonga saved early break points to force a first-set tie-break, in which he acrobatically hurdled the net and flashed a 220 kilometre (136 mile) per hour serve before edging it 8-6.

The two exchanged breaks early in the second and Australian Open runner-up Tsonga produced a leaping forehand volley as he saved three more break points at 2-3.

But Davydenko buried a winner on break and set point at 5-4, with Hawkeye confirming he clipped the baseline to level the match at one set each.

As Tsonga tired, Davydenko broke immediately in the third set and looked on course for a quick finish until the French world number seven produced an audacious drop shot to save match point on his own serve.

He then bamboozled Davydenko with another backhand drop to break for 5-4 and whistled a second-serve ace past the Russian to level it 5-5 and pump up the Chinese crowd.

Tsonga was in the ascendancy but the renaissance came juddering to a halt in the decisive tie-breaker as he double-faulted and committed a series of errors to implode 0-7.

The 'fifth Grand Slam,' featuring the top eight players, is making a fourth and final appearance at Shanghai's state-of-the-art Qi Zhong Stadium before moving to London as the ATP World Tour Final.