(Reuters) - Britain's Andy Murray reached the semi-finals of the ATP World Tour Finals when he completed his Group A matches with a 6-2 7-6 victory over Jo-Wilfried Tsonga on Friday.

Big rival Novak Djokovic clinched top spot in the group earlier against Tomas Berdych and Murray walked on to the O2 Arena court knowing winning one set would be enough to see him finish runner-up to the Serbian world number one.

Frenchman Tsonga, despite losing his opening two round-robin matches, could have reached the semis at Murray's expense with a straight sets win but a loose start scuppered any hope.

Murray surged into a 4-0 lead as a languid Tsonga gifted the Scot two service breaks with a rash of unforced errors.

Tsonga finally got off the mark in the fifth game but it did little to alter the flow of the match as U.S. Open champion Murray wrapped up the opening set in 33 minutes.

Two double faults from Tsonga helped Murray break serve at the start of the second. Murray appeared to lose focus when he allowed Tsonga to break to love and level at 4-4.

Another sell-out crowd at the famous London venue were treated to some entertaining rallies as Tsonga, with nothing to lose, went for broke but Murray avoided using up any extra energy when he claimed a second set tiebreak 7-3.

Murray will face Roger Federer in the semi-finals as long as the Swiss, who is already through, avoids a straight sets defeat against Juan Martin del Potro in Group B action on Saturday.

(Reporting by Martyn Herman, editing by Meadows)