ATP World Tour Finals
Venue: O2 Arena, London Date: 22-29 November
Tournament coverage: Live on BBC Two, 28/29 November, 1415/1430 GMT; every match live on BBC Radio 5 live/5 live sports extra; live text commentaries on BBC Sport website; live coverage every day on Sky Sports
By Piers Newbery
BBC Sport at the O2 Arena
Juan Martin del Potro beat top seed Roger Federer to reach the reach the semi-finals of the ATP World Tour Finals and knock out Andy Murray.
Federer knew that a win of any kind would put him through with Murray, while Del Potro needed a straight-sets win to qualify with the Scot.
But in the event, Del Potro won 6-2 6-7 (5-7) 6-3 to take both men through and leave Murray helpless as it came down to the percentage of games won by all three men.
Such was the utter confusion over the qualification system that Del Potro was left waiting in the O2 Arena with thousands of fans to find out if he had made it, and he even indulged in a knock-up with Argentina football star Carlos Tevez.
When it was finally revealed he had gone through to the last four, Del Potro said: “It’s an incredible moment, my first Masters semi-final, I’ve nothing to lose.”
Murray had earlier missed his opportunity to guarantee qualification with a straight-sets win over Fernando Verdasco, the Briton needing three sets before eventually battling past the Spaniard.
606: DEBATE
“What a shambles from the ATP at the end as they kept Del Potro waiting before finally revealing that he had gone through”
BBC Sport’s Oliver Brett
Amid the various qualification possibilities, it was easy to forget that Federer was facing Del Potro for the first time since the Argentine’s stunning US Open final win in September.
The 21-year-old had brought an end to Federer’s five-year unbeaten run at Flushing Meadows with a display of spectacular power, having lost all six previous matches against the Swiss.
And the signs were not good for Federer from the opening moments as he made a shocking error after a net cord, netting an attempted drop shot with Del Potro stranded and the empty court gaping.
Federer was fortunate to save two break points as his opponent made unforced errors but the Swiss helped him out with a wayward forehand of his own on the third.
Matters then got significantly worse for the world number one when he fell a double-break down in game five with a double-fault.
Del Potro served out the set confidently enough and could sense the straight-sets win he needed to knock Federer out at the start of the second.
Federer was hugely fortunate when facing another break point to see a snatched forehand volley thump into the tape and dribble over the net.
It was the only significant opportunity for either player before they arrived at a tie-break, and Del Potro gave an early reminder of that US Open final with two forehand winners.
Federer recovered an early mini-break but netted a makeable volley and Del Potro had two serves for the match.
However, he missed them both with errors and Federer pounced with four successive points to level the match, pumping his fist in celebration, perhaps knowing that - statistically - he had all but qualified.
Federer had the edge as the decider progressed but could not convert any of three break points in game seven, and Del Potro made him pay in the following game before serving out the victory with an ace after two hours and six minutes.
Del Potro and Federer move on to Saturday’s semi-finals, where Robin Soderling, Nikolay Davydenko or Novak Djokovic will be waiting after group B concludes on Friday.
Earlier, fifth seeds Frantisek Cermak and Michael Martinek defeated eighth seeds Mariuisz Frystenberg and Marcin Matkowski 6-4 6-4 to reach the semi-finals of the doubles.