Murray and Nishikori played the longest three-set match in ATP World Tour Finals history – the Scot eventually prevailing 6-7 (9/11) 6-4 6-4 after three hours and 20 minutes.
The first set alone took 85 minutes, Nishikori winning it on his fifth set point, but Murray’s well of fighting spirit never runs dry and he dug himself out of several holes on his way to a 21st consecutive victory.
It is the first time since the tournament moved to London’s O2 Arena in 2009 that Murray has won his opening two matches, and he is in pole position to reach the semi-finals from John McEnroe group.
Should he win the group, he would avoid Djokovic in the semi-finals, setting up the mouth-watering prospect of a final on Sunday with the No 1 ranking on the line.
Murray said: “I think for the tournament and stuff, for everyone interested in tennis, that would probably be the perfect way to finish the year.
“For me and I’m sure for Novak, both of our goals would be to try to win the event. For him, whether that’s by beating me, someone else, or, for me, if it’s winning against Novak or another player, it doesn’t change for us as players.”
For all Murray’s achievements during 2016, this was the first time he had played a top-five opponent since losing to Djokovic in the French Open final in June.
And it would have been no surprise to Murray that this turned into an epic encounter.This was his fourth meeting of the year against Nishikori and two of the previous ones, in Davis Cup in March and the US Open in September, were five-set marathons.
The Scot headed for the ice bath afterwards in a bid to recover for tomorrow’s match against Stan Wawrinka.
Meanwhile, Djokovic will take on alternate David Goffin in his final group match after Gael Monfils (rib) pulled out.