Gold Trip ($21) raced to a two-length win from Emissary ($26) with Gold Emocean ($41) a further 1-¼ lengths away third.
Zahra was questioning whether Gold Trip would run the journey, however Maher and Eustace did give the jockey a lot of confidence.
"They're the best trainer of stayers," Zahra said.
"That's one thing I had confidence in, that they trained it.
"I was actually quite vocal that I didn't think he'd get the trip and thankfully my good mate Jamie Spencer didn't have much luck on him. It was probably just the perfect lead-up run."
A Caulfield Cup winner before teaming with Eustace to claim a Cox Plate and now the Melbourne Cup, Maher said the team behind Gold Trip needed to be thanked for their efforts.
Gold Trip was one of five runners for the stable in Tuesday's race – with stablemate High Emocean finishing third – and Maher said the success had not yet sunk in.
"Everyone's had a lot to do with this horse," Maher said.
"(Farrier) John Bunting, he's had this horse in very good order all the way along.
"He's quite dicey, this horse, and he's done a fantastic job. He's a great mate, great bloke and he's very good at what he does.
"Dave and my brother (Declan), everyone, it's just huge. Dave and I are lucky enough to stand up here and most of our staff are here today along with friends and family.
"It's just fantastic."
Eustace said since arriving in Australia in 2014 he did not imagine ever winning the race.
"Obviously you know the race, that it exists, a bit later in my life," Eustace said.
"But ever since I've been here this is the race you want to be contesting and just getting the chance to do that, to win it, is quite extraordinary."