Novak Djokovic & Milos Raonic reach ATP World Tour Finals semis

Goffin played Djokovic after Gael Monfils withdrew with a rib injury

Novak Djokovic kept up the pressure in the race for the year-end number one ranking with victory over Belgian David Goffin at the ATP World Tour Finals.

Djokovic had already qualified for the semi-finals, and completed the group stage with a 6-1 6-2 win.

Milos Raonic joined the Serb in the last four with a 7-6 (7-5) 6-3 win over Austria's Dominic Thiem.

Murray won his first two group matches and plays Stan Wawrinka on Friday at 14:00 GMT.

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Five-time champion Djokovic took his record at the O2 Arena to 21 wins in 22 matches with a straightforward dismissal of Goffin.

The Belgian, 25, was in London as the alternate, and making his tournament debut after Gael Monfils withdrew with a rib injury.

With £144,000 and 200 ranking points on offer for every group match victory, there was plenty to play for, but Goffin was outclassed by the champion.

Djokovic broke serve at the second attempt and the most significant drama came when he argued with umpire Fergus Murphy and tournament supervisor Tom Barnes over a time violation.

"One time!" the Serb said repeatedly, unhappy that he had not been given a warning he was getting close to breaking the 25-second rule.

It did nothing to interrupt the momentum on court as Djokovic eased to victory in just 69 minutes.

"Undoubtedly, I felt the most comfortable today from all three matches I've played this week," said Djokovic.

"I felt like I increased the level and the quality of tennis, so that's a good sign."

Djokovic now has a rest day before he plays Murray, Wawrinka or Kei Nishikori in Saturday's semi-final.

"No stress at all," he added. "Why stress? We come here to play, to enjoy.

"This is one of the biggest tournaments in the world. I'm just having fun on the court."