Roger Federer made it a clean sweep in the Boris Becker Group at the ATP World Tour Finals with victory over Marin Cilic.

Federer maintains perfect record

Federer maintains perfect record

The Swiss legend, who had already secured his semi-final spot ahead of the contest, was put through his paces against an opponent whose elimination from the tournament had been confirmed after defeats in his two earlier matches.

Croatia's number one managed to take the first set 7-6, winning the tie-break 7-5, and he was just one set away from beating Federer for just the second time in his career, having previously met on eight different occasions.

However, the 19-time Grand Slam champion battled back to take the next set 6-4 before romping home in the decider 6-1, securing a three-set victory and maintaining his 100 percent record going into the semi-finals.

The 36-year-old, who is unable to overhaul Rafael Nadal at the top of the world rankings before the end of the year, is aiming to win the Tour Finals for the seventh time and also for the first time since 2011.

Elsewhere, the final Boris Becker Group match will see Alexander Zverev and Jack Sock go head-to-head on Thursday night with the winner booking their place in the last-four stage of the tournament.