Milos Raonic opened his ATP World Tour Finals campaign with a routine victory over Gael Monfils at London's O2 Arena on Sunday.

The Canadian, a beaten Wimbledon finalist against Andy Murray in July, won 6-3 6-4 in his first match of the Group Ivan Lendl, which also includes Novak Djokovic, who came from behind to defeat Dominic Thiem earlier in the day.

Ranked two places above his opponent at world number four, the combination of Raonic's powerful serve and his control from the baseline was more than a match for the mobility and creativity of his entertaining but inconsistent French opponent, who made two double faults to be broken in his first service game.

"[That] was very tough, we all know Milos is a big server," Monfils said in an on-court interview.

"You need a very big return and I was unable to do it. Hopefully next time I will be able to."

That early break proved damaging to the hopes of Monfils and when he was broken again in the seventh game of the second set, all that was required of Raonic was to serve out the match in relative comfort.

The decisive second break arrived following a high-quality exchange of forehands starting at the baseline.

Both players began to trade backhand slices as they moved into the court, only for Raonic to demonstrate ice-cool shot selection to wrong-foot Monfils and plant an easy winner into the empty advantage court. 

"He played some great tennis and there was some great tennis on the court," Raonic said.

"I have to be very happy with that. It was a great pleasure to be back here after two years. It's fun until you get burned in one of those entertaining points. 

"I'm happy with the way I played, I'm happy with the way things went."