Federer won his 70th title in his 100th final. Picture - Reuters.

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Roger Federer fought his way to a sixth season-ending championship after defeating Jo-Wilfried Tsonga in the ATP World Tour Finals.

It was the Siwss' 100th final, and he marked the occasion with deserved 6-3 6-7 (6-8) 6-3 win - his 70th title.

The 16-time grand slam champion had to work for his victory though, and despite cruising through the first set, he was held-off in an enthralling second set, missing out on a match point in the tie-breaker against an exciting Tsonga .

Federer stepped it up in the third though, displaying all his grace and class, much to the delight of the 17,500 capacity crowd at London's O2 Arena.

The 30-year-old went on to take the set with ease and looks determined to make ground on Novak Djokovic and Rafael Nadal.