World No. 1 Serbian star Novak Djokovic booked a spot in Sunday's semifinals at the season-ending ATP World Tour Finals.

The 2008 champion went 3-0 in his round-robin matches in London after handling fifth-seeded Czech Tomas Berdych 6-2, 7-6 (8-6) at The O2 Arena.

Djokovic prevailed in 1 hour, 37 minutes with the help of seven aces and was broken only once on Day 5, as the former Wimbledon runner-up Berdych fell to 1-2 for the week. Djokovic saved three set points in the second stanza.

"It was quite a close set," Berdych said. "I had some chances in the tiebreak. It wasn't one of my best matches with him."

The two-time year-end No. 1 Djokovic has now won his last nine matches against Berdych and is 11-1 lifetime against the powerful Czech.

Friday's other round-robin match will pit third-seeded Andy Murray (1-1) against seventh seed Jo-Wilfried Tsonga (0-2), who was last year's Tour Finals runner-up to the great Roger Federer.

Round-robin play will wrap up on Saturday when the second-seeded former No. 1 and reigning Wimbledon champion Federer (2-0) takes on sixth seed Juan Martin del Potro (1-1) and fourth-seeded David Ferrer (1-1) battles eighth seed Janko Tipsarevic (0-2). Ferrer was last week's titlist at the Paris Masters. Del Potro was the Tour Finals runner-up in London in 2009 and upset Federer in a final last month in Basel -- Federer's hometown.

The 31-year-old 17-time Grand Slam champion Federer is a record six-time Tour Finals champ, including wins in the last two finals in the prestigious eight- player event.

This week's four-player Group A features the group winner and Australian Open champion Djokovic, the U.S. Open and Olympic titlist Murray, Berdych and Tsonga, while Group B boasts 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 Monday in London.

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