Jamie Murray and his Brazilian partner Bruno Soares will finish the year as the world's top-ranked doubles pair.
The duo went into the ATP World Tour Finals trailing Nicolas Mahut and Pierre-Hugues Herbert by 575 points but overhauled them on Thursday courtesy of their third win.
The French duo were eliminated after losing both their first two matches but could still have prolonged the race by winning their final group match against Henri Kontinen and John Peers.
But they lost 6-7 (5/7) 6-4 10-4, meaning Murray and Soares cannot be overtaken.
Murray became the first British player ever to be officially ranked world number one when he moved to the top of the individual doubles rankings earlier this year, pipping brother Andy to the honour.
Soares could now finish the year with that title if he and Murray win the title on Sunday.
Mahut only needed one victory to become the first French player to finish a year ranked number one but the Wimbledon champions have been well below their best at the O2 Arena.
Murray and Soares will play either Feliciano Lopez and Marc Lopez or Raven Klaasen and Rajeev Ram in the semi-finals on Saturday.