Marcus Fraser was in disbelief at the penalty call that helped Rangers beat the Buddies 4-0 at Ibrox.
St Mirren went behind early in Glasgow but steadied the ship before Antonio Colak went down in the box under pressure from Declan Gallagher.
Referee Nick Walsh was adamant it was a spot-kick, with James Tavernier doubling the hosts lead at a crucial point in their Premiership clash on Saturday.