Murtagh said: “It's all the hard work everybody does at home. It's me knowing the kind of horse it takes to win these races, like when I was riding in them.
“I'm going back to my experience as a jockey. That's the kind of horse we need for this track or that race.
“The last time he ran here he ran very well, and I liked the way he came home. He came on for that run, and that gave us confidence.
“He's out of a good staying mare. Fair play to Ben. He was good.”
Sonnyboyliston is entered in the Comer Group International Irish St Leger at the Curragh on September 12, while Murtagh also nominated him for the Melbourne Cup at Flemington on November 2.
An Australian trip has not been ruled out, but Murtagh's sights are set on the Curragh for now.
He said: “I have him in the Irish St Leger, and we'll have to think about that first now before we consider Australia.
“Last year when he won (on) Irish Champions weekend over a mile and a quarter, I always thought when he stepped up in distance he'd get better.
“At the start of the year I thought he might end up in the Ebor. It doesn't always work out like that, but today it did — by a head.
“He is a pretty good stayer. He has to improve a lot for the Irish St Leger — but he's probably going to get a hike for that. It's the next logical step.
“There have been a lot of people looking at him before today, and I'm sure they will be on again after today, but my plan is to go for the Irish St Leger.”