London [U. K], Nov.15 : Playing his first match as world number one, British tennis maestro Andy Murray produced a rich vein of form to clinch a straight-set victory over Croatia's Marin Cilic in the round robin clash at the ATP World Tour Finals here on Tuesday.

The 29-year-old, who ended Novak Djokovic's 122-week reign at the top of the rankings last week, broke his Croatian opponent twice in each set on his way to a 6-3, 6-2 victory in the one-sided contest that lasted one and a half hour.

It was Murray's 12th win over Cilic and 20th victory in a row.

Murray and Serbia's Djokovic are vying to end the year at the number one spot.

Earlier, Murray battled past American John Isner to claim his maiden title at the BNP Paribas Masters and become the second-oldest player since John Newcombe in 1974 to debut at World No. 1.

In another men's singles clash, fifth-seed Kei Nishkori also made a winning start to the tournament by sealing a 6-2, 6-3 win over Swiss star Stan Wawrinka.(ANI)