The 20-year-old Halifax-born player shot an opening round 69 to lie joint second in an international field of 78 players.
Bolton-born Ben Eccles, who now lives in Victoria, showed the way with a 66.
English amateur champion Marsh, who took top honours at the 2014 Halifax Courier sports awards evening last November, made a flying start with an eagle on the par five second hole.
He gave both shots back with a six on the eighth but had birdies on 10, 12 and 15 to post his excellent score.
Marsh is one of three top amateurs representing England Golf in big Australian events throughout January.
English stroke play champion Ben Stow (Rushmore, Wiltshire) shot 75 and reigning South American amateur champion Paul Howard had a 73.
After the Royal Melbourne event, the trio move on to the Lake Macquarie International at Belmont, the Australian Amateur Championship at The Australian and The Lakes golf clubs and then the New South Wales Medal at Monash and Killara.