London - World number one Roger Federer dug deep to begin his ATP World Tour Finals campaign with a hard-fought 4-6, 7-5, 6-1 victory over Spain's Fernando Verdasco on Sunday.
Federer briefly faced the unpalatable prospect of a third successive defeat as Verdasco took the first set in commanding style.
But the Wimbledon champion, who had lost his previous two matches in Basel and Paris, edged a tight second set before hitting his stride to take the final set with ease.
Collecting his record-breaking 15th grand slam title with a dramatic win over Andy Roddick at Wimbledon just a month after landing his first French Open title guarantees that 2009 will always hold fond memories for Federer.
But the 28-year-old's surprise US Open final defeat to Juan Martin del Potro in September has left him keen to re-establish his supremacy by ending the year top of the world rankings.
Federer, who can still be replaced as number one by Rafael Nadal, has cut a lacklustre figure since that defeat to del Potro, losing in the Basel final to Novak Djokovic and then crashing in his next match against Julien Benneteau at the Paris Masters.
Verdasco, 26, is appearing in the Tour Finals for the first time after enjoying the best season of his career. The left hander reached three ATP finals, as well as making it to the Australian Open semi-finals, and he started impressively here.
A double fault on the opening point set the tone for Federer, who was broken immediately. He found it difficult to cope with Verdasco's sliced serves and never got close to breaking back.
Committing 16 unforced errors hardly helped his cause and Verdasco easily served out the first set.
The second set was tighter as Federer gradually found some rhythm. The turning point came when Verdasco misjudged an overhead return at 5-6 down, allowing Federer to convert his first break point and take the set.
Federer, a four-time winner of the Tour Finals, had finally shaken off his lethargy and broke again in the second game of the final set.
Suddenly he was transformed and a series of perfectly placed forehand winners broke Verdasco's resolve in emphatic fashion.
His victory means Federer will play British number one Andy Murray in his next Group A match, while Verdasco will play del Potro.