The 20 year-old made no mistake rifling home the winner nine minutes from time.
The victory means they travel to Drumahoe for Friday night’s second leg full of confidence.
The winners of this two-legged tie, of course, will take on Carrick Rangers home and away next week for a place in the Premiership next season.
Manx Grand Prix: Michael Dunlop gears up for Classic Superbike victory bid on new Team Classic Suzuki GSX-R750
Jeremy McWilliams notches Bishopscourt double at Classic Bike Festival Ireland on Michael Dunlop's Team Classic Suzuki
Kofi Balmer 'feels amazing' after making dream move to Crystal Palace
In Pictures: Team NI's Commonwealth Games medal winners
Blackpool reject bid for Shayne Lavery amid Millwall speculation
The home side, who started the better went close on 18 minutes as Michael O’Hanlon’s centre found Dean Youle and his effort was superbly kept out by a fully stretched Marty Gallagher.
On 30 minutes a slick counter attack by the visitors ended with Stephen Curry feeding Michael McCrudden, who in turn slid the ball inside to Sammy Morrow, but after the striker skipped around goalkeeper Paddy Flood, he was unable to get his shot away and he was crowded out.
Gallagher was called into action on 57 minutes as Chris Trussell’s 25 yard free-kick was tipped over by the ’Stute net-minder. Minutes later a McCrudden free-kick from the right deep to the back post found Niall Grace, but he headed narrowly wide.
Soon after another McCrudden’s free found Mark Scoltock, his header back across goal was headed onto the bar by Stephen O’Donnell.
The visitors went close to breaking the deadlock on 69 minutes but Morrow’s 20 yard strike was superbly tipped over by Flood.
Comrades broke the deadlock on 81 minutes as McMullan blasted home low into Gallagher’s bottom right hand corner, to spark wild celebrations amongst the home support.
In the closing stages ’Stute had a great chance to level things and score a crucial away goal, but Dean Curry’s close range header was straight at Flood.
Meanwhile, Newry City won 4-0 at Armagh City in the first leg of the promotion/relegation play-off between the Championship and the Premier Intermediate League.
Ballyclare Comrades: Flood, Brown, Gray, McMullan, Woods, Youle, O’Hanlon, Dobbin, Trussell, Lynch (Johnston 77), Robinson (D Taggart 66).
Institute: Gallagher, O’Donnell, McDermott (Roddy 73), Scoltock, D Curry; Foy, Grace, McCrudden (Friel-Curran 85); S Curry, Morrow, Brown (McIntyre 65).
Referee: Mr Shane Andrews (Comber).