Muddel converted an Asmat El Ouargui pass for the only goal at Colney for David Williams' team just before half time. City's rearguard action in the second half was epitomised by Andrew Cave-Brown, who was named man of the match.
Midfielder Tom Miller was dismissed for Norwich with ten minutes left when he collected a second yellow card, while Town's Cathal Lordon suffered the same fate moments later.