Roger Federer started his bid for a record sixth title at the ATP World Tour Finals with a 6-2, 2-6, 6-4 victory over France's Jo-Wilfried Tsonga on Sunday. Federer's triumph at London's 02 Arena 12 months ago moved him level with Pete Sampras and Ivan Lendl on five titles in the end of season finale and he is determined to successfully defend his crown after a frustrating campaign. The 30-year-old, down to fourth in the world rankings, will finish the year without a Grand Slam title for the first time since 2002, but he arrived for 2011's concluding tournament in good form after back to back titles in Basel and Paris. Although he gave a slightly erratic performance to kick off his 10th successive Tour Finals appearance, he has now won 13 matches in a row and 18 of his past 19 and his rivals among the world's top eight players will be rightly wary of Federer in this kind of mood. Federer suffered arguably the most stunning meltdown of his career when he last met Tsonga in London in the Wimbledon quarterfinals earlier this year. For the first time in a Grand Slam the Swiss star was beaten after holding a two set lead. But he was finally back to his dominant best a week ago in the Paris Masters, which he won by defeating Tsonga in the final for his second victory over the French number one since that loss at the All England Club. Federer, who had former Arsenal star Thierry Henry sitting in his box at courtside, picked up where he left off in Paris and took the first set here in emphatic fashion. Tsonga didn't help his cause with two woefully mistimed forehands to present Federer with the first break in the fourth game. Federer never looked likely to relinquish that advantage and he wrapped up the set with another break after Tsonga double-faulted at 0-30 and then netted a half-volley. Yet Tsonga's remarkable capacity to switch from subdued to inspire in the blink of an eye reared its head again at the second set. Previously so lacklustre, Tsonga suddenly found his rhythm and broke for a 2-1 lead when Federer's forehand drifted wide. Federer looked rattled by the improved accuracy and power of Tsonga's ground-strokes and continued to make careless errors as the Frenchman secured another break before serving out the set. Tsonga was able to save a break point with a booming forehand at 2-3 in the final set, but Federer had a little more momentum now and gradually wrestled control back from his opponent. The decisive moment came when Tsonga served to stay in the match at 4-5. Federer unloaded some blistering ground-strokes to earn three match points and Tsonga couldn't stem the tide as the Swiss clinched a hard-fought victory. World number two Rafael Nadal will play America's Mardy Fish, making his Tour Finals debut, in the other Group B match later on Sunday.