(CNN) -- World number one Roger Federer had to battle from a set down to beat Spaniard Fernando Verdasco 4-6 7-5 6-1 in their Group A opener at the ATP Tour Finals in London on Sunday night.
Federer looked in danger of a third straight defeat as Verdasco breezed through the opener and threatened a massive upset in the second set.
But the Swiss maestro began to exert more pressure on his opponents service at the back end of the set and broke through in the 12th game on his first set point.
The decider was a formality as Federer, who had never dropped a set previously to Verdasco, broke him twice and threatened a whitewash until the world number seven held in the sixth game.
But the end was inevitable as four-time finals winner Federer served out to love to claim a deserved victory which puts him on course for the semifinals although a tough match against Andy Murray awaits on Tuesday.
"I never really found the range in the first set and got a bit lucky at the end of the second set, but in the third I played great," he told Sky Sports.
Earlier, home hope Murray gave the finals the perfect start with a 6-3 3-6 6-2 victory over U.S. Open champion Juan Martin Del Potro in their Group A match.
It was a crunch encounter to kick off the elite eight-man tournament, with only one place separating them in the world rankings, but Britain's Murray dominated the decider to delight his home crowd at the O2 Arena.
World number four Murray made a blistering start as he took a 5-0 lead in the first set with his Argentine opponent needing treatment for a nose bleed.
Suitably restored, Del Potro made Murray work to claim the opener and then took charge in the second as he led 3-0 and 5-2 before closing it out to level.
But Murray dominated the decider, breaking Del Potro in the second game to take a 4-1 lead.
Del Potro double-faulted in the eighth game to set up two match points for Murray as the Scot converted the second with a backhand winner.
"It was always going to be tough. I played well today, started really good, he came back into it but I stayed tough in the third set," Murray told Sky Sports after his crucial victory.
In-form Novak Djokovic, the defending champion, and world number two Rafael Nadal begin their Group B play on Monday with Nikolay Davyedenko and Robin Soderling also in action.