The Group 1 Turnbull Stakes (2000m) was also considered before the Waller stable settled on The Bart Cummings and its 'Golden Ticket'.
Ridden by Jye Mcneil, Valiant King ($61) appreciated the fast pace in scoring by 2-¾ lengths from Torranzino ($71) with the $2.15 favourite Gilded Water a neck away third.
Gilded Water, with Jamie Kah aboard, carved out a solid tempo, and at one stage led by a conservative seven lengths, but could not withstand the finishing burst of the winner in the final 200m.
Charlie Duckworth, representing the Waller stable, said Valiant King appreciate the solid tempo but the stable had been unsure as to the gelding's fitness ahead of Saturday.
"Fitness was our biggest concern which is why he held a nomination in the Turnbull as well as this," Duckworth said.
"He was much better suited to this in terms of grade and also distance.
"We were really unlucky to miss the Sydney Cup in the autumn when he had a minor foot issue leading into it and we just thought he was primed and ready to go, but hey, it will be much better to win a Melbourne Cup than a Sydney Cup."
McNeil thought his task of overhauling the leader Gilded Water looked unlikely when the field turn the corner for the 500m run home.
"I thought we had a big task ahead of us," McNeil said.