Portadown lost a 3-1 half-time lead during the NIFL Youth League Section A visit to Institute Colts.
The 5-3 defeat at the final whistle has pushed the Ports down to ninth in the table, rather than a fourth-place reward for victory.
Brendan Litter’s first-half brace and a Peter Campbell finish put Chris Wright’s players in control.
However, Institute scored four second-half goals without reply.
Portadown lost out by 6-0 away to Crusaders in the latest NIFL Reserve League match.
Gary McCullough’s players will take on Carrick Rangers next in the league with a November 18 road trip.