Djokovic takes on Tomas Berdych first on Friday, and victory for the world No 1 would mean any sort of win for Murray over Jo-Wilfried Tsonga would see the Scot reach the semi-finals.
But if Berdych wins in straight sets, Murray must beat Tsonga without losing a set to advance.
That should not be beyond him - Murray has won six of his eight previous meetings with the athletic but erratic Frenchman, including their last five matches.
The first year the tournament was held at the O2 Arena, 2009, Murray appeared to have done enough with his two round-robin victories but results conspired against him and he ended up missing out by one game.
"We're not really used to it in tennis because we play knockout everywhere else," said Murray. "But that's just the way this tournament's always been.
"There's no point in changing it. That's the tradition of this tournament. It's absolutely fine. You need to try and view it like it's a knockout and try to win the first couple of matches, get yourself safe if you can.
"We should be able, as professional sportsmen, to deal with all those sorts of situations, be able to focus and concentrate regardless of the situation."
His fellow Briton Jonny Marray is already through to the last four with doubles partner Freddie Nielsen after they won their opening two matches to ensure they will top their group.
Today they have the luxury of a dead rubber against Sweden's Robert Lindstedt and Romania's Horia Tecau, who they beat in the Wimbledon final.