Grunnie — affectionately known as ‘Munch’ — fired rounds of 69 and 73 for a level par 142 total to finish two shots clear of closest rival Liam Carruthers (72-72).
Powfoot greenkeeper and holder Neil Hamilton had set the early pace in the competition when he shot a superb five-under-par 66 in the opening round.
But playing partner Grunwell stuck to his guns and steady golf saw him triumph as Hamilton slumped to an 81 in the afternoon.