LONDON - Roger Federer moved into the Olympic semi-finals on Thursday as the Wimbledon champion cut giant American John Isner down to size with a 6-4, 7-6 (7-5) victory on Centre Court.

Federer had to be at his most patient in the face of a barrage of big serves from the 6ft 9in Isner, but the world number one was finally able to produce just enough magic to move into the last four of the Olympics for the first time since the 2000 Games in Sydney.

The 30-year-old, bidding to win his first singles gold medal, will play Argentina's Juan Martin del Potro for a place in the final.

Since winning the longest match in tennis history against Nicolas Mahut at Wimbledon in 2010, Isner has embarked on a steady climb up the world rankings and he claimed a shock win over Federer in the Davis Cup earlier this year.

Isner's massive serve kept Federer at bay for much of the match, but the 17-time Grand Slam champion eventually found a way through in the ninth game of the first set.

Isner had to hammer down two successive aces to save break points, but

Federer earned a third and this time the American dragged a routine forehand well wide to surrender the first break.

Even then Federer found it hard finish off Isner and he had to save a break point himself before finally serving out the set.

With Isner firmly in the groove on serve and Federer just as obdurate on his own serve, the second set was another tense affair and it needed a tie-break to decide it.

There was little to seperate them in the breaker, but Federer held his

nerve and got a stroke of luck at the vital time as his return on his first match point clipped the net and bounced down on the other side just out of Isner's reach.

(AFP)