Del Potro beats Federer to send Murray crashing out

JUAN Martin Del Potro earned a second successive win over world number one Roger Federer to deny Andy Murray an ATP World Tour Finals semi-final berth by the slimmest of margins.

ROARING SUCCESS: Juan Martin Del Potro earn his semi-final spot by a whisker - to the dismay of Andy Murray (Getty Images)

Federer knew that if he won he would go through with Murray, while Del Potro needed a straight-sets victory to qualify with the British number one.

And Del Potro came within two points of sending Federer crashing out but the 15-time Grand Slam champion clawed back the second set tie-break to take the match into a decider.

But the Argentinean earned the crucial break in a thrilling final set to win 6-2, 6-7, 6-3 and leave the group standings decided on percentage of games won - with Del Potro progressing ahead of Murray by just one game to reach the end-of-season semi-finals for the first time.

"It's an incredible moment and I'm very happy to do it here in London with this crowd," said Del Potro.

"i've improved my game a lot and now I will play my first semi-final and I've got nothing to lose."

Del Potro made a name for himself by claiming his maiden Grand Slam title with a five-set victory over Federer at the US Open in September.

And, with the pair meeting for the first time since, Federer went into the match saying he wanted "revenge" for that defeat - but it was Del Potro who emerged in ruthless form.

The 21-year-old got off to the perfect start by capitalising on a sluggish opening game from Federer to steal an early break.

Del Potro earned another break point in the fifth game with a sublime cross-court backhand and 28-year-old Federer, who struggled to control his serve from the moment he stepped on court, handed Del Potro a 4-1 advantage with a double fault.

Del Potro was firing on all cylinders and closed out the set with ease and looked to have taken that form into the second with a break point in the opening game.

Federer - four-time winner of the end-of-season tournament - held serve as he began to find his rhythm but failed to break Del Potro as both players held serve.

Del Potro raced out of the blocks in the tie-break and Federer was facing an early exit when he trailed 4-2.

But the Swiss player fought back in sensational style to level the match and take it to a tense final set.

Del Potro needed to win the final set by a margin of 6-3 or better to progress and it looked like it would be Murray going through with the score at 4-3 to Del Potro but with Federer on serve.

But Del Potro broke Federer at the crucial moment to lead 5-3 before closing out the match and leaving the O2 Arena in stunned silence.