Two quickfire goals from the visitors gave them the advantage at the 35-minute mark, before Rowan Roache’s penalty halved Brig’s deficit at half time.
Kieran Charnock then levelled for Brig with a powerful header, before Chris Marlow was shown a straight red card for a foul on Jack Mackreth.
Tony Gray thought he had won it for Warrington with a goal in the 89th minute, before Allen’s late leveller.
Brig started the brighter of the two sides, Allen’s effort in the first minute fizzing past the post.
Jamie Milligan’s men continued to have the majority of the ball in positive areas, but the opening goal went to the visitors on 28 minutes.
Warrington won a free kick after a foul on the left-hand side, and Jack Dunn’s free kick went beyond Danny Roccia in the Brig goal.
The Yellows made it two just three minutes later, when Mackreth ran through and struck an effort which Roccia was only able to parry into the bottom corner of the net.
Roccia was then called into action again on 40 minutes, doing well to get in the way of a well struck effort from Thomas Warren.
Brig were then presented the chance to equalise from the spot in added time when Sheldon Green was brought down just inside the area.
Roache stepped up and sent his penalty straight down the middle for his second goal in two games.
Brig carried that momentum through to the second half, with Danny Wisdom firing over and Green putting an effort narrowly wide.
There was then drama on 61 minutes when Marlow was shown a straight red card for impeding Mackreth during a driving run towards goal.
Despite being a man down, Brig continued to push for the equaliser and came close on 79 minutes when Matt Dudley’s effort was deflected behind.
They then came close again on 81 minutes when Green’s ball in was pushed over the bar by Tony McMillan.
From the subsequent corner, Kieran Charnock arrived first to power the ball into the corner to equalise for 10-man Brig.
The home side then piled on the pressure as Allen saw an effort well saved, before the Warrington put in several last-ditch blocks to deny Brig from a corner.
It was the visitors that re-took the lead on 89 minutes, however, Gray getting in behind the Brig defence before sliding the ball past Roccia.
But it was Brig and Allen who would have the last word, the number 11 firing home into the bottom left corner from the edge of the box to spark jubilant scenes amongst the home faithful.