Britain's double Wimbledon winner and back-to-back Olympic champion coasted to a 6-3, 6-2 win as he began life at the top of the global rankings.

Murray has never won the season-ending tournament which invites the top eight players in the standings, and will be hoping to stay as world number one in front of Serbian rival Novak Djokovic, who he replaced at the summit earlier this month.

His ascent to the top followed consecutive tournament victories in Beijing, Shanghai, Vienna and Paris and he proved far too strong for Cilic as both players contested their first match in the John McEnroe group in the hard court tournament.

The Scot traded breaks with the seventh seed at the beginning of the first set but then clicked into gear with some fine strokes to move into the lead.

Murray then needed an ace to save a break point at the beginning of the second set, and he then powered home by serving out to love.

"It is one of the best matches I have played here over the years," said Murray.

"I will try to keep going to the end. 

"When you start winning your matches, you gain confidence.

"On the break points I was a little bit more solid.”

In the first game of the day, Japan's fifth-ranked Kei Nishikori upset Swiss third see Stan Wawrinka, 6-2, 6-3.

The Ivan Lendl group will continue with the second matches for the players involved tomorrow.

Djokovic, the number two seed and defending champion, takes on fourth seed Milos Raonic of Canada with both looking for a second win.

Frenchman Gaël Monfils and Austrian Dominic Thiem will square off with both players looking for an opening success.