A Douglas side with an average age of just 20 overcame stiff resistance at Oldershaw to bag a 22-15 win.
First half tries from Niall Killey, Bryn Snellgrove and Conor McCoghan saw Douglas 15-12 in front at half-time.
Snellgrove added another after the break which was converted by Tom Chamberlain and this was enough to seal the game.
Johnny Stewart wins Senior Manx Grand Prix
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54-year-old won in commanding fashion
Johnny Stewart wins Junior Manx Grand Prix
The race was declared after lap two due to a red flag incidentÂ
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