Jamie Murray and Bruno Soares maintained their perfect record at the ATP World Tour Finals to march through to the semi-finals.
After winning their first two matches, Murray and Soares only needed a set against Ivan Dodig and Marcelo Melo to guarantee a place in the last four.
But they went one better by winning the clash 6-3 3-6 10/6, setting up a semi-final meeting on Saturday against either Raven Klaasen and Rajeev Ram or Feliciano Lopez and Marc Lopez.
It was significant because the 200 ranking points they earned put Murray and Brazilian Soares provisionally ahead of Nicolas Mahut and Pierre-Hugues Herbert in the race to finish the year as the number one team in the world.
The French pair can move back ahead when they play their final match on Friday but their semi-final chances have already gone so reaching the final would definitely be enough for Murray and Soares.
Saturday could potentially see Jamie and Andy Murray both clinch year-end number one crowns, an unprecedented achievement for two brothers.
Andy said: "It would be amazing to do that. It's obviously unlikely to happen. It's not all in our hands. I don't know if that's happened before. I wouldn't imagine so. It would be nice to finish the year that way."
David Beckham and son Romeo were among the crowd at the O2 Arena to watch Murray senior reach the semi-finals for the first time on his second appearance.
He and Soares, the Australian and US Open champions, have been excellent so far and they wasted little time securing the set they needed.
But Soares dropped serve in the eighth game of the second to allow Brazilian Melo and Croatian Dodig to level matters.
That meant the match would be decided on a first-to-10 tie-break, and Murray and Soares opened up a gap that was never closed.
Murray admitted it was hard to put the qualification scenarios out of his mind.
He said: "We knew we had to win I think seven games, which is a weird kind of mentality to go into the match. We played great the first two matches.
"Of course, we really wanted to win because we wanted to get the points to try to get closer to number one. Mentally, I don't know, it was an odd situation for us.
"I think we did well to win. We played some good stuff at the right moments. Really happy to have won three matches, be through to the semis."
The 30-year-old also welcomed the presence of Beckham, saying: "He obviously likes tennis. His son's really into it as well. I think he's a big fan.
"It's good for tennis when guys like that come out to watch the events. There's been a lot of people here this week, famous faces from the sporting world. It's good for us. I think it gives everyone a little buzz."
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