Former champion Novak Djokovic and world No. 3 star Andy Murray were Monday's round-robin winners at the $7.125 million season-ending ATP World Tour Finals.

The world No. 1 Australian Open champion and French and U.S. Open runner-up Djokovic handled seventh seed Jo-Wilfried Tsonga 7-6 (7-4), 6-3 indoors at The O2 Arena. The Serbian star prevailed in 1 hour, 39 minutes by holding his serve throughout on Day 1.

Djokovic, who will finish as the year-end No. 1 for a second straight year, captured this event in Shanghai in 2008, while Tsonga was last year's Tour Finals runner-up to the great Roger Federer.

Meanwhile, the U.S. Open champion, Olympic gold medalist and Wimbledon runner- up Murray overcame fifth seed Tomas Berdych 3-6, 6-3, 6-4 in Monday's opener in London. Murray struck 28 winners en route to a 2-hour, 17-minute victory.

"He served very well on a lot of the break points, especially in the first set. He started to miss a few more first serves in the second and third sets when I had my chances," Murray said. "That sort of helped me get into the point and find a way of being aggressive, using some variety, whereas some of the time in the first set he just completely overpowered me."

On Tuesday at The O2, the second-seeded reigning two-time Tour Finals champion and former world No. 1 Federer will battle eighth seed Janko Tipsarevic and last week's Paris Masters titlist and former Tour Finals runner-up David Ferrer, seeded fourth this week, will tangle with former runner-up and sixth seed Juan Martin del Potro at this elite eight-player tournament.

This week's four-player Group A features Djokovic (1-0), Murray (1-0), Berdych (0-1) and Tsonga (0-1), while Group B boasts the record six-time winner and former Tour Finals runner-up Federer, Ferrer, del Potro and Tipsarevic. The top-two players from each group will play in the semifinals on Sunday, and the winners will square off in the lucrative finale next Monday in London.

The 2012 World Tour Finals champion can earn as much as $1.76 million.