The son of Oasis Dream made a winning debut at Kempton in September and stepped up again to remain unbeaten.
He was settled towards the rear by jockey Dane O'Neill where he travelled smoothly.
Dane swtiched around the whole field, avoiding trouble by making his run up the centre of the track. Mushir showed a decent turn of foot to take the lead before holding off No Leaf Clover to win by a head.
Roger said: "He is a colt we have always liked and he has always worked nicely at home. He has done well to win against more experienced horses and is an exciting prospect for next year."