What a decision it was, as he collected a clearance header 20metres out on the right hand side, and with a first time volley, fired a shot that gave the keeper no chance.
Locals described it as a contender for goal of the season.
After that he left the field and was replaced by new signing Connor Taylor from Melville.
With 15 minutes to go, Fencibles got on the scoreboard after a messy goal mouth scramble resulted in Alex Thurton poking one over the line. The goal breathed new life into the home side but City United keeper Tom Pamment, with a man of the match performance, denied everything they attempted, aided by the post and crossbar at times.
The good luck was on the visitors shoulders and they held on to their one-goal advantage until the full-time whistle.
This Saturday's home fixture against Lynn Avon will be the last for the season for super striker McNab. He scored 28 goals for the Blues last season and so far this season has nine.
He and his partner will be returning to the UK for an indeterminate time so supporters are asked to show up in big numbers to give him a great send-off. Kick-off at Links Avenue is at 2.30pm.