The Stoke loanee, introduced in place of Michael Symes after 61 minutes, netted within 15 minutes of coming on to give the O's local bragging rights.
After an uninspiring first half, both teams showed more enterprise after the interval and it was the visitors who initially created the better chances.
Jonathan Douglas had a powerful free-kick tipped over the bar by Ryan Allsop, who then turned a shot from Jake Bidwell past the post.
But it was the introduction of Brunt that awakened the hosts' as an attacking force and after 75 minutes it paid dividends.
Former Brentford midfielder Martin Rowlands played the ball into Brunt, who took the ball on his chest, turned and slid a left-footed shot past Simon Moore.