But Blues coach Young slammed the attitude of his side at Edgeley Park and is set to ring the changes for their European clash at Calvisano on Saturday.
Young said: "We have had consistency in our selection over the last few weeks but there were very few good performances. Only the players off the bench like Nicky Robinson, Robin Sowden-Taylor and Deiniol Jones did well and we will have to have a re-think.
"The players need to look at themselves. The urgency, desire and hunger just wasn't there and despite winning, we let ourselves down. It was a poor performance and we got out of jail."
Replacement wing Mustoe pounced from Jamie Roberts' pass but he had not even been included in the Blues' 22 until
Darren Allinson fell ill on the eve of the ie in Stockport.
Young added: "Darren had a chest infection and we didn't have another scrum-half in the squad. There wasn't enough time to bring someone up from Wales so we put Richard on the bench. We are lucky he was there."