Andy Murray began life as the world number one with a convincing victory over Croatia’s Marin Cilic at the ATP World Tour Finals in London.
The Briton, who replaced Novak Djokovic of Serbia at the top of the rankings last week, won 6-3 6-2 at the O2 Arena for his 20th win in a row.
Murray and Djokovic are vying for the year-end number one spot.
Japan’s Kei Nishikori beat Swiss Stan Wawrinka 6-2 6-3 in Monday’s other John McEnroe Group match.
The evening session saw Murray step onto court as the world number one for the first time – and he delivered the result that most of the 17,000 spectators wanted.
“A big thank you for all of the support, it was an incredible atmosphere today,” Murray said as the crowd saluted him. “I really appreciate it.”
Both men misfired from the baseline in the early stages, with Murray making two winners to 14 unforced errors in the first set, but it was a similar story across the net.
The Scot, 29, took his chances when they came, breaking twice and coming through despite four double faults.
There were more signs of the form that has brought Murray such success this year as the second set unfolded.
After saving an early break point with an ace, the Wimbledon champion broke at 2-2 thanks to two mighty forehand winners, and again at 4-2 with another heavy cross-court forehand.
Murray, who has yet to win this title, put his erratic start to the match down to the pace of the court, rather than any added tension.
“I didn’t feel any more nervous than usual,” he said.
“It’s just quite different conditions in there than what we’ve been practising in during the week. It’s a lot slower than it has been.
“I think maybe some of the errors at the beginning were more getting used to playing in new surroundings again.”