Juan Martin del Potro has squeaked into the semifinals of the ATP World Tour Finals by beating Roger Federer 6-2, 6-7 (5), 6-3, knocking out Andy Murray.

That result means Del Potro and Federer both advance after a three-way tie in Group A. All three players finished the round-robin stage with two wins and identical 5-4 set records.

Murray was eliminated after winning the lowest percentage of games. Had Del Potro lost just one more game against Federer, the Scot would have advanced at the Argentine's expense. Murray beat Fernando Verdasco 6-4, 6-7 (4), 7-6 (3) earlier on Thursday.

Del Potro easily beat four-time champion Federer in the first set in London's Millennium Dome, but the top-ranked Swiss rebounded and won the second set in a tiebreaker. In the decider, Federer and Del Potro held serve through 3-3, meaning the Argentine needed to win the next three games to advance along with Federer.

He held, then broke Federer for the third time in the match, and then held again to ensure advancement.

"I'm in the semifinals. I'm happy for that," Del Potro said. "But [it] was strange."

Federer's spot in the semifinals was assured when he held serve to make it 1-1 in the third set, but he said he didn't know that at the time.

"Otherwise I would have gone on the ground and celebrated it, right?" the 15-time Grand Slam champion said with a smile.

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