
He endured a torrid run back in the field under Mark du Plessis, but rallied in the straight to win the 2350 metre contest by a length.
Munce revealed the race was hard to watch and he had all but given up hope.
"I was nearly going to walk back to the horse stalls," Munce said.
"But Mark knew what he was doing. I didn't."
First Crush runs for well known Sydney owner Max Whitby, and Jenny Moses, the wife of another former jockey-turned trainer Kevin Moses, who trained the horse for his first five starts.
Whitby was a part-owner of Savabeel who Munce rode to win the 2004 Cox Plate.
"I told Max we would win the Grafton Cup and it's terrific to do it for him," Munce said.
"But it's a big team effort. I've got a lot of young kids, a lot of young staff who work tremendously hard."
A $100,000 purchase for Kevin Moses from the 2014 Magic Millions Patinack Dispersal, First Crush has won seven of 34 starts earning in excess of $358,000.
First Crush is a half-brother to South American Group I winner Questing New from Brazilian Champion 3YO Filly Loving New (Brz).
He is the 15th stakes-winner for Aquis based Husson (Arg), who stands at their Queensland base at a fee of $9,900 this spring. He was popular last year covering 96 mares and again looks a value choice for an outcross sire completely free of Danehill blood.