London, England -- (Sports Network) - Roger Federer captured a fifth ATP World Tour Championship Tuesday by way of his come-from-behind, three-set victory against Scot Andy Murray in Group A play at the season-ending ATP World Tour Finals in London.

Federer dropped the first set but rallied for a 3-6, 6-3, 6-1 triumph to ensure his year-end No. 1 ranking over Spaniard Rafael Nadal, who held the honor last year but lost to Sweden's Robin Soderling Monday in his round- robin opener. The five-time Tour champion Federer tied Jimmy Connors' mark and is just one shy of Pete Sampras, who ended as the top-ranked player for six straight years from 1993-98. Federer was champ from 2004-07.

The Swiss sensation moved to 2-0 in the round-robin and is seeking his fifth title of the year with one more match in group play against U.S. Open champion Juan Martin del Potro, whom he lost to in the season's final grand slam event.

The Argentine star also pulled out a three-set victory Tuesday over Spain's Fernando Verdasco in Group A by way of a 6-4, 3-6, 7-6 (7-1) final. Del Potro lost to Murray in his first match on Sunday and will take on Federer to close out group play on Thursday. Verdasco lost to Federer in his first match of the tournament.

Although Federer now stands as the lone player from Group A with two wins, he has to either defeat del Potro or depend on a number of scenarios to unfold before punching his ticket to the semis. The Swiss, Murray and del Potro could tie atop the group at 2-1 should the Argentine be victorious and Murray defeat Verdasco.

Murray's service game suffered after taking the opening set allowing Federer to even the match. The Swiss then won the final six games of the match to take the second straight meeting between the two in one hour and 57 minutes.

The Scotsman had taken four straight decisions between the two before Federer broke through in the semifinals of the Western & Southern Financial Group Masters in August. The head-to-head series still favors Murray by a 6-4 count.

Del Potro was unable to convert a pair of match points in the third set, as Verdasco fought back to force a tiebreaker. A number of Verdasco unforced errors allowed del Potro to dominate the tiebreak, and another forehand error by the Spaniard ended the match after two hours and 24 minutes.