London, England - Six-time champion Roger Federer and British home favorite Andy Murray were a pair of round-robin winners Tuesday at the season-ending $6 million ATP World Tour Finals in London.

The second-seeded Wimbledon runner-up and former world No. 1 superstar Federer handled fourth-seeded U.S. Open finalist Kei Nishikori 6-3, 6-2 in 69 minutes at The O2.

Federer, who improved to 3-2 lifetime against Nishikori, including 2-1 this year, smacked seven aces and was not broken on Day 3, while his Japanese counterpart coughed up his serve three times en route to defeat.

"I was expecting a very difficult match," Federer said. "I've know him [Nishikori] since he was 17 years old and always thought he was a great talent and he's going to have a great future. I'm very pleased with the way I played."

Federer improved to 2-0 in the four-player Group B with his tour-best 70th match win of the year, while Nishikori dropped to 1-1 for the week.

Federer, who is making a record 13th consecutive appearance at the Tour Finals and has an outside chance of capturing the year-end top ranking, holds the record for the most titles at this exclusive event.

If Federer were to qualify for his 12th career Tour Finals semifinal, it would tie the record set by Ivan Lendl. The 33-year-old Swiss icon would also be the oldest player to advance to the last four since 2003 runner-up Andre Agassi.

The fifth-seeded Murray (1-1), meanwhile, snuck past seventh-seeded Milos Raonic (0-2) in straight sets, 6-3, 7-5, in just over an hour-and-a-half in Tuesday's Group B nightcap. Murray broke Raonic to grab a 6-5 edge in the second set and then closed out his Canadian counterpart with a big hold.

Murray tallied three breaks, compared to only one for Raonic.

Surprisingly, all six matches so far this week have ended in straight sets.

Murray will battle Federer on Thursday.

Wednesday's round-robin action will come from Group A, as world No. 1 and Wimbledon titlist Novak Djokovic (1-0) will take on third-seeded Australian Open champ Stan Wawrinka (1-0) and sixth-seeded former Wimbledon runner-up Tomas Berdych (0-1) will face sixth-seeded U.S. Open champ Marin Cilic (0-1).

The reigning two-time and three-time overall Tour Finals champion Djokovic topped Rafael Nadal in last year's finale in London. The 27-year-old star is two wins away from clinching the year-end No. 1 ranking for the third time in four years.

Nishikori, Raonic and Cilic are making their Tour Finals debuts this week.

Round-robin action will be staged here through Friday, followed by the semifinals on Saturday and lucrative final on Sunday.