Andy Murray wins on his debut as World No. 1, beats Marin Cilic at ATP Finals

The Wimbledon champion was tested for much of his opening match at the ATP finals but still came out on top, playing in his home country and beating Marin Cilic 6-3, 6-2 Monday at the O2 Arena.

Taking the court as the No. 1-ranked player for the first time, Andy Murray got the job done.

Great Britain's Andy Murray celebrates after winning his round robin match against Croatia's Marin Cilic. (REUTERS)

The Wimbledon champion was tested for much of his opening match at the ATP finals but still came out on top, playing in his home country and beating Marin Cilic 6-3, 6-2 Monday at the O2 Arena.

“It was obviously nice to play in that stadium with the crowd like that. It obviously helps,” Murray said. “After a long, kind of, few months, it’s nice to know that I’m going to be finishing the year playing in that sort of atmosphere.”

Murray took over at the top of the rankings last week, replacing Novak Djokovic. But the year-end No. 1 ranking is still up for grabs and could be decided on Sunday if both Murray and Djokovic reach the final.

The prospect of attaining that, however, doesn’t seem to be weighing too heavily on Murray’s mind.

“The last few days, I haven’t thought about it too much,” Murray said. “It didn’t change much for me.”

It certainly hasn’t affected his ability to win matches. Murray has won a career-high eight titles this season, including a second Wimbledon title in July and a second straight Olympic gold medal in August. Since then, he has won titles in Beijing, Shanghai, Vienna and Paris.

“When I need to step in, I didn’t. When I need to wait a little bit longer, I wasn’t waiting,” said Cilic, the 2014 U.S. Open champion. “The hitting could have been better. Yeah, a little bit unfortunate to go 6-3, 6-2 down, where it felt it was much, much closer in the first set. Beginning of the second, I had couple chances as well.”