Defending champion Roger Federer made a winning start at the ATP World Tour Finals with 6-2, 2-6, 6-4 victory in his opening round-robin match against Jo-Wilfried Tsonga at the O2 on Sunday.

The Swiss, competing at the season-ender for the 10th consecutive year, raced through the first set in 21 minutes but world number six Tsonga made sure the capacity crowd got value for money with a stirring fightback.

Federer missed two routine forehands in the third game of the second set to gift Tsonga a break of serve and the French powerhouse suddenly came to life, breaking the Federer serve again on the way to levelling the match.

The decider went with serve until the final game when Tsonga wavered badly, missing a routine volley, then serving a double fault to give Federer sight of victory.

A crunching forehand brought up three match points for the 16-times grand slam champion and although Tsonga saved one with a first serve winner he could only watch as Federer rolled a backhand winner down the line on his second attempt.

Federer, whose world ranking has slipped to four after a rare season without a Grand Slam silverware, will set a new record if he retains the title in London.

The 30-year-old is currently level on five with Ivan Lendl and Pete Sampras.

Later on the opening day Rafa Nadal takes on debutant Mardy Fish of the United States, also in Group B.