US Open champion Andy Murray battled his way to an edgy opening win against Tomas Berdych at the ATP World Tour Finals in London.
Murray began the round-robin stage with a 3-6 6-3 6-4 victory at the O2 Arena.
He saw 10 break points and the first set slip away before finally converting his 11th chance and going on to win in two hours and eight minutes.
The top two players from each group will progress to the semi-finals of the season-ending championships.
"In indoor matches, when both of us served pretty well and weren't losing too many points on our first serve, it can hinge on a couple of points here or there," said Murray.
"A lot of the break points I didn't waste. If you watched them back he served very well on a lot of them, especially in the first set."
Murray has yet to make it past the semis in three previous attempts at the London venue, but he arrived this year on the back of that breakthrough win in New York and an Olympic gold medal in the summer.
A near-capacity crowd of 17,000 greeted the return of Britain's first male Grand Slam champion since 1936, but once the action got under way it was edginess that prevailed over excitement.
Berdych was among his victims at Flushing Meadows and the Czech fifth seed, who went into the match with a 4-3 record against Murray, had been keen to gain revenge for that semi-final defeat.
Murray's coach, Ivan Lendl, was courtside for the first time since New York and his charge began brightly enough, thumping a backhand return past Berdych on the opening point.
He could not put his man away so decisively on the break points that followed though, with a 0-40 lead disappearing in game five. Berdych was playing well when it counted.
With frustration mounting on the Briton's side of the net at seven missed opportunities, it came as no great surprise when Berdych made the breakthrough to lead 4-2 after the Scot netted a forehand.
One break proved enough to secure the first set and Murray was in deep trouble at 0-40 early in the second, but the roles were reversed this time as the world number three fought his way to safety and fashioned another three break points in game four.
When they too went begging, and with memories of missed match points at his last three tournaments still fresh, Murray looked ready to explode, but Berdych helped him out with a wayward forehand on break point number 11 and finally the home favourite was in the ascendancy.
The crowd had been subdued for the most part as the man the majority were supporting felt his way into the match, but he began to attack the Berdych second serve and that brought him the decisive break in game three of the final set.
With his serve increasingly dominant there were no alarms for Murray as he saw out his final four service games to secure an important opening win, with further round-robin matches to follow on Wednesday and Friday.
"I think the biggest moment was in the second set, at 1-1, when I had break point," said Berdych. "I hit a forehand return and it was [just] out.
"Who knows, it could have been 2-1 with an early break after winning the first set. There was a pretty good chance, but it didn't happen."
Asked how it felt to step onto a British court as a Grand Slam winner, Murray said: "It was a good atmosphere. For me it's important in the last week of the year, when everyone's a little bit tired, to have that atmosphere, the big crowd, to give you that extra little push that you need to play good tennis.
"So it was good to be back playing in the UK."
In the first doubles match of the tournament second seeds and defending champions Max Mirnyi and Daniel Nestor beat fourth seeds Robert Lindstedt and Horia Tecau 6-4 6-7 (1-7) 12-10.
Group B gets under way on Tuesday, with Roger Federer taking on Janko Tipsarevic and David Ferrer up against Juan Martin del Potro.