Red Cadeaux had worked his way to the lead with just a few hundred meters to run over the Flemington course but Dunaden, with substitute rider Christophe Lemaire up, found enough to get up in the final jump and win by a nose.
Lemaire picked up the mount at the last minute because Dunaden's regular rider, Craig Williams, was suspended owing to a careless ride last week at Bendigo. A last-minute appeal Monday failed.
That was forgotten in the heat of battle that concluded Australia's biggest race. Lucas Cranach, who also was prominent early in the stretch run, finished third, 1 1/4 lengths back of Red Cadeaux. Last year's winner and the early favorite to repeat, Americain, got home a neck farther back in fourth.
Dunaden, trained by Mikel Delzangles for Qatari Sheik Fahad al-Thani, finished in 3:20.84 over going rated good. The 5-year-old, French-trained son of Nicobar now has six wins from 19 lifetime starts. Tuesday's score was by far his richest payday.
"There are no words for this," Lemaire said in the winner's enclosure. "I want to thank everybody for the emotion and the passion they have. It is my first time in Australia but I love Flemington. You know, races like the Japan Cup, Breeders' Cup, Epsom Derby and the Melbourne Cup -- these are the big ones everybody wants to win."