That was the nailbiting situation at London's O2 Arena as three of the planet's top tennis players were left clueless as to whether they had made it through to the semi-finals of the season-ending ATP World Tour Finals.
Two of them had qualified from Group A - Del Potro and Federer, as it turned out - with Murray edged out of the five-million-dollar tournament by the tightest of margins on an ATP statistics boffin's calculator.
"Anyone know what's going on? I think I'm audi (out) but the rules aren't worded too well," Murray wrote on his Twitter microblogging page.
With all three tied on matches won and percentage of sets won, it went down to games.
The Briton won 44 out of 87 games played (50.57 percent), while Del Potro won 45 out of 88 (51.14 percent). Federer, who won 44 out of 84, was relatively in the clear on 52.38 percent.
Murray had beaten Spain's Fernando Verdasco 6-4, 6-7 (4/7), 7-6 (7/3), which, barring Argentina's Del Potro first beating Swiss world number one Federer, doing it in three sets, and winning a certain number of games in the process, would have been enough to see him through.
But sure enough, Del Potro defeated Federer 6-2, 6-7 (5/7), 6-3, with a final set that saw Federer through after having won one game, and at 3-3 Del Potro having to win it 6-3 to go through.
As the Argentine shook hands with Federer, neither player, to answer Murray's question, had any idea what was going on.
"Sure, it's confusing," Federer said. "I asked Juan Martin myself at the net, Did you make it or not? He said, 'I don't think so'. So that's the story I got."
Federer was in the locker room, having a doping test, "showering, stretching and stuff when I heard I was through." Del Potro said his coach Franco Davin "told me I qualified 25 minutes after the match, because nobody knew what happened."
Murray was still up into the night twittering. Federer said: "With the other two guys, it's quite incredible. I am surprised it came down to a couple games. "There are certain rules and these are the rules.
Sometimes unfortunate, sometimes fortunate. These times are very hard for Murray, who didn't get through. But he got so close."
"How can we imagine that we all play three sets and it comes down to a couple of games? Del Potro beat the number one player in the world, and I guess also deserves to go through. There's only two places, and that's the way it is. It happens very, very rarely," Federer said.
"It definitely was quite a rollercoaster match for the ones who were there with the calculators. "I wasn't one of them!" he joked.
Del Potro, the world number five, said: "This is sport. Just two players have to qualify.
"It's difficult to do the numbers because Roger, me and Murray won two matches, and unfortunately Murray -- he's out. So it's strange for us, but we like it."
Murray revealed that part-way through his third set, he asked whether the calculations were done on the number or percentage of games won.
"I don't actually think that it's that complicated. It's not that hard to work out the percentage," he said of the tournament rules.
"But everyone - I don't know why - makes it sound so complicated. Whoever has the best set percentage goes through. If not, it goes down to the percentage of games. The people that go through are the ones that deserve to."
Federer topped Group A, and will now play the runner-up from Group B tomorrow.
Sweden's Robin Soderling has qualified for the semis, while Russia's Nikolay Davydenko and Serbian title-holder Novak Djokovic are battling today for the group's other spot. The French and Australian Open champion said he had no preferred opponent.
"I'm excited to be through. But I wished I could have won. That would have given me extra confidence," Federer said. "Now it's the way it is. But I've got a day to rest, which is probably a little advantage."
US Open champion Del Potro is wary of world number three Djokovic.
"All players are playing very good this season. They are very strong," he said.
"Djokovic for me could be the most dangerous. But Robin has a good serve. Davydenko is so fast. Everyone has good things to play against me.
"But, well, I qualified. I'm in the semi-finals. I'm happy for that. But it was strange."