Saltonstall hit the jackpot to land the Colm Quinn BMW Mile Handicap, the feature race on Day Two of the Galway Festival.
On his sixth start for Adrian McGuinness, having run a number of good races when with Michael Halford and Godolphin, the five-year-old raced towards the rear through the early stages, with stablemate Aussie Valentine cutting out the running.
Colin Keane's mount still had plenty behind him three furlongs out, but could be spotted travelling well in his cheekpieces and made smooth progress.
Picking up well when asked, the 9-1 chance stayed on strongly to score by half a length from Innamorare, who just held the fast-finishing Quizical by a head for second. Rufus King was fourth.
McGuinness said: "I can't believe it, and it is great for the crew who have worked hard and for (owners) the Dooley brothers from Manchester and Bart O'Sullivan, who is also our yard sponsor.
"Today was a plan, some of these plans don't come out, but this has and it is brilliant.
"Stevie (Thorne), my assistant, is brilliant at picking out these horses and picked him out at Goffs and we looked at him.
"He'd had a few problems and had bled a few times, but he said he was a horse we could take a chance on and we always felt Galway was a fantastic place to be in, so we tried to get him up for Galway and it has happened."
The winner also holds entries tomorrow and Sunday.
Fast Buck dominated from start to finish in the Colm Quinn BMW Novice Hurdle to take Listed honours for Willie Mullins and Paul Townend.
A 10-length winner at Listowel last time out, the strapping sort bounded into an early advantage as Townend attempted to stretch the field out.
Only Davy Russell on Charles Byrnes' Turnpike Trip was still in contention jumping the last, but Fast Buck kept up to his work to win by a length and a quarter as the 2-1 favourite.
Townend said: "He was good in Listowel, it was hard to read into it what he beat that day, but the manner in which he did it was nice and he is building on that and ran into a fair one (Fakir D'Oudairies) on his first run at Cork.
"He disappointed us at Naas, but is getting his act together now and is a big, scopey horse who will jump a fence in time."
Elsewhere, smart novice hurdler Zero Ten made a winning start over the bigger obstacles in the Latin Quarter Beginners Chase.
Trainer Emmet Mullins said of his 1-2 favourite: "You have to have a big engine to be able to win these races.
"He's very well balanced. He's on the ball. He's clever. He was a bit cautious at a few fences, but on his first run over fences you'd expect that. He's a bit special."