Luke Dobie's 78th-minute header secured City Under-21s victory at Millwall.
In a game dominated by the visitors, Alex Russell's men had to wait until 12 minutes from the end for the all-important breakthrough.
Former AFC Wimbledon loanee Toby Ajala set up the decisive goal with a teasing cross which Liverpudlian Dobie - fresh from signing an extended contract - was able to nod home.
Coach Alex Russell said: "It's a win we thoroughly deserved and in truth we should have scored more. It could have been three or four-nil at half-time.
"The lads deserve credit for their persistence in sticking to the game plan and we got our reward with Luke's well-worked goal."
City Under-21s: Carey; Battersby, J.Wilson, Jones, King; Dobie, Bryan, Reid; Burns, Krans (Jordan 78), Ajala. Subs not used: Castenheira, John, Batten, Mitchell.