LONDON (Reuters) - World number one Roger Federer started slowly put finished like an express train Sunday as he beat Fernando Verdasco 4-6 7-5 6-1 in his opening match at the ATP World Tour Finals.

Spaniard Verdasco deservedly won his first ever set against the Swiss as Federer sprayed errors early on and he had a glimmer of a chance at 5-5 in the second before the match swung.

Federer, who can secure the year-end top ranking in the season-ending showpiece, broke Verdasco in the 12th game of the second set and quickly raced away to victory.

Verdasco, making his debut at the tournament, capitulated tamely in the end and will need to beat Juan Martin del Potro in his second Group A match to keep his hopes of reaching the semi-finals alive.

(Reporting by Martyn Herman, Editing by Peter Rutherford))