With just nine minutes remaining and the home side pressing hard for a first-leg advantage to take to Gigg Lane on Sunday afternoon, full-back Neil Ashton chased down a harmless through ball toward the Shrewsbury penalty area.
But in playing the ball back to keeper Luke Daniels, it flicked off the head of the advancing keeper and, to the astonishment of everyone looking on, the ball bounced into an empty net.
It was cruel for Ashton who had an otherwise excellent game and tough too on Shrewsbury who dominated for long periods of an often exciting encounter.
They found their way to goal blocked by a stubborn Bury defence and also by visitors goalkeeper Wayne Brown, who pulled of a number of important saves.
After missing out on automatic promotion by just one goal, Bury went into the game with a 12-match unbeaten record to protect, while Shrewsbury began the evening undefeated in four games since losing at Bury on Good Friday.
Boosted by their impressive 2-1 success at Dagenham last weekend which finally clinched their play-off place, the home side began brightly and were quickly posing problems for the Bury defence.
After one or two early scares, there was a close call for the visitors on 22 minutes when central defender Efe Sodje almost deflected a Chris Humphrey cross into his own net.
But it was Brown who did well on 33 minutes when he saved at point-blank range from Ben Davies and when the ball was returned into the box, top scorer Grant Holt saw his low drive strike a post.
Following the break, Paul Simpson's men continued to hold the upper hand and when Holt headed a Davies corner into the goalmouth, the Bury defence only just survived the ensuing scramble.
In fact, Bury had settled for a draw when they took the lead in such unexpected circumstances.
But even after falling behind, Shrewsbury still managed to create a shooting opportunity for Davies that fizzed over, while Brown distinguished himself again right at the death by saving brilliantly from Holt.