ATP Finals: Novak Djokovic beats Juan Martin del Potro in semis

Novak Djokovic proved his powers of recovery once again by fighting back to beat Juan Martin del Potro in the semi-finals of the ATP World Tour Finals.

The world number one came back from a set and break down to win 4-6 6-3 6-2 at London's O2 Arena.

With the year-end top ranking assured, the Serb now has the chance to cap 2012 with his second season-ending title.

Djokovic will face Roger Federer in Monday's final after the Swiss beat Andy Murray in the second semi-final.

"I believed that I could come back," said Djokovic. "I believed that I could turn this match around in my favour and I've done so.

"I've played, from that moment on when I got the break back, very flawless tennis. That makes me very happy and also confident before the final."

Djokovic had come through the round-robin stage with three wins and was keen to stress that his desire to take the title outdid any end-of-season fatigue.

However, the sight of Del Potro repeatedly winding up arguably the biggest forehand in the game would have been enough to excuse any opponent pining for the off-season.

Del Potro blasted his way to safety with his two trademark shots - a big serve and a thunderous forehand - when facing early break points, and Djokovic was soon being forced out of his comfort zone in the baseline exchanges.

A woeful attempt at a smash in game seven suggested the pummelling was having an effect and for the next six games it was all Del Potro - a running forehand winner getting him two break points at 4-4 and another heavy blow from that side converting the second.

The first set was wrapped up after 47 minutes and things looked bleak for Djokovic at the start of the second set as the assault continued from across the net.

Del Potro narrowly failed to break in the opening game but made amends at the next opportunity, setting up three more break points at 0-40, and this time the world number one succumbed.

Far from signalling the end of the contest, however, it prompted a repeat of Djokovic's group stage match against Murray as the Serb found his best game in adversity.

He hit back immediately to level at 2-2, and suddenly the effects of Saturday's win over Federer appeared to take their toll on Del Potro.

With his energy levels apparently dipping, the sixth seed's second serve became vulnerable to Djokovic's fearsome return and the unforced errors began to rise.

Djokovic racked up eight of 10 games as he took control of the match, levelling at one and getting the decisive break - to love - to lead 2-1 in the third.

Del Potro was now being mercilessly worked from side to side and the seemingly unstoppable world number one showed he too can hit a screaming forehand to break once again.

A quickfire love service game ended Del Potro's resistance after two hours and 11 minutes and took Djokovic through to his first final at the O2.