Fourth in the Group I ATC Australian Derby to Jon Snow and then second in the Group I SAJC South Australian Derby to Volatile Mix, the Ciaron Maher trained Ruthven was cherry ripe to make it third time lucky.
He was given a perfect rode by Hugh Bowman, who positioned his mount behind the speed before easing out into clear running with 800 metres to run.
Ruthven strode to the front before the turn and turned the race into a one-act affair, bolting clear to win the 2200 metre staying test by nearly four lengths over the up and comer Rockstar Rebel, a son of dual Derby winner Rebel Raider.
"Amazing win," Bowman said.
"I took a lot of confidence out of riding him on Tuesday morning. I knew he had a strong will.
"He's been known to sort of be a little immature, letting horses run past him, wanting to chase again but I just tried to keep his mind on the job and didn't he deliver in flying style."
Retained to race by his breeders, Ruthven has the impressive record of three wins and five seconds from 10 starts with prizemoney of $763,900.
Maher said Ruthven "could be" a spring cups horse, but the astute trainer said time would tell if that's in 2017 or the years ahead.
"He's still got to grow and develop a bit more and whether it's this year or next year, I'd say he'll be thereabouts at some stage," Maher said.
"He's always been a late maturer. He's just starting to furnish as a racehorse really.
"Great effort by the team, it's a third Derby for this horse and it's a great effort to keep him up."
The 15th stakes-winner for Domesday and his third Group I winner, Ruthven is the best of five winners from unraced Ruddigore, a daughter of the great champion and AJC Derby winner Octagonal.
Ruddigore comes from the family of Group II winners Cangronde and Fiery Venture, but will have no further impact as Ruthven is her final foal as she died in 2015.
Ruthven is the second Derby winner for Domesday, who is also the sire of Group II WATC West Australian Derby winner Arcadia Dream, while another of his star performers Doctor Doom won the Group I ATC Spring Champion Stakes.
A versatile sire, completely free of Danzig blood, Domesday produced stakes-winners over a wide range of distances and stands at Aquis Farm at a fee of $8,800.