Former World No.1 Andy Murray scripted a fine comeback from a set down to upset Denis Shapovalov in the first round of the Dubai Tennis Championships, but said he "probably doesn't have too long left" in his career.

Murray refused to be written off and held firm for a three-set win 4-6, 7-6(5), 6-3 against Canada's Shapovalov to seal his 500th tour-level victory on a hard court.