The third seed seemed to be on the edge of victory when serving 7-5 5-4, but some bad play by Murray allowed Janowicz to capitalise and he certainly took full advantage of Murray's mistake.
Towards the end of the game Janowicz certainly seemed to dominate the match winning 5-7 7-6 6-2 to reach the quarter-finals at the Paris Masters.Andy Murray will now be heading to the ATP World Tour Finals in London which begins on Monday (5th November).
Murray has never been further than the quarter-finals at the Paris Masters and this year he looked set to improve his record at the Paris tournament.
In the second set, a blistering forehand return from Janowicz's serve seemed to give Murray a decisive breakthrough at 4-3.
A regulation win seemed imminent when Murray moved 30-0 and then the match point at 5-4, only for some careless forehands to allow Janowicz back into the match with his first match of the day.
He controlled the tie-break from the outset and broke twice in the decider as Murray's challenge faded dramatically. Murray seemed to land a couple of blows but it wasn't enough and Janowicz held his nerve to serve for the win of his career.