• ATP World Tour Finals

Federer fights back to stun Del Potro

Only once has Roger Federer failed to make the semi-finals © Getty Images

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Roger Federer showed why he is a record six-time champion at the ATP World Tour Finals after producing a sensational comeback against Juan Martin del Potro to qualify for the last four in London.

A victory for either player would have seen them join defending champion Novak Djokovic, year-end world No. 1 Rafael Nadal and tournament-debutant Stanislas Wawrinka in the semi-finals at the O2 Arena.

The Verdict

• Roger Federer did something this afternoon that he has not been able to do throughout the season: Win matches ugly.
• The Swiss has had a difficult campaign, but he always saves his best performances for the ATP World Tour Finals, and that was what hit Juan Martin del Potro full in the face in a scintillating shootout for a spot in the semi-finals.
• Federer has been second-best to opponents in situations when he needed to be at his best, but when he found himself behind against Del Potro, the Federer of old appeared at the O2 as Roger roared with plenty of emotion during the match, and fed off the wonderful support.
• Will it be good enough against Rafael Nadal tomorrow in the semi-finals? Well, if this match is anything to go by, Federer will take heart from the fact he can still come up with the goods when his back is well and truly against the wall.

And it was Federer who delighted his supporters by fighting from a set and two breaks down to win 4-6 7-6(2) 7-5, taking seven of the last nine games to topple the Tower of Tandil in a pulsating encounter to set-up a semi-final showdown with Nadal on Sunday.

The majority of the O2 crowd were on Federer's side, but they were stunned into silence in the opening game as Del Potro made a lightning start to the match by getting the immediate break.

In the pair's third meeting in as many weeks, Federer was making plenty of errors on his forehand, and the Swiss squandered his opportunity to hit straight back when reaching 30-30 in the following game.

A sloppy fifth game from Federer gifted Del Potro the cushion of a second break - and the Argentinian did so on the back of taking five consecutive points from 40-0 adrift.

At 5-2 Del Potro blew his chance to close out the first set on serve as a fine forehand winner from Federer sparked a mini-comeback. After showing his delight with a fist pump to have two break-back points at 5-4, instead it was Del Potro who was celebrating after fending them off with monster aces at 127mph and 134mph en route to taking the set.

Federer fell a break down in the third game of the second set when he struck the net, but after losing three of the opening four games, the Swiss recovered with three games on the spin to lead for the first time in the match at 4-3.

Twice Federer forced Del Potro to remain in the set at 5-4 and 6-5, and on both occasions the Argentinian held on to take it into a tiebreak. However, Federer attacked his opponent to claim the mini-break to go 2-1 in front, and from that point he never looked back as he stormed to the set at 7-2 to stay in the tournament.

The momentum disappeared from Federer in the final set as Del Potro benefited from yet another forehand error from his opponent to open-up a 3-0 advantage.

Federer returned the favour to reclaim the break and level at 3-3, but Del Potro ended the run to resume the lead at 4-3. The following two games were shared, and it was down to Federer to hold serve to stay in the match.

The 17-time grand slam winner remained calm to once again square the contest, and raised his game to take a 6-5 lead with a break, before rounding off the remarkable recovery by saving a break point and sealing the win with an ace down the middle.

On being behind in the final set, Federer revealed he was "slightly angry" and had thoughts that his season could be coming to a disappointing end.

"I was thinking it was going to be over soon. I thought 'Here we go again'," Federer admitted. "I was really getting angry with myself. I tried to stay focused for it not to happen, and it didn't. To get the victory was a great feeling, and I am very happy."

Del Potro was left disappointed with the loss, saying: "I had two chances to win the match, but he played great and he deserved to come back in both sets. I made the mistakes and he was focused to take the chance, and I think that was the key of the match."

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