The Henry de Bromhead-trained gelding made all in the extended two-mile-five contest and the 16/5 shot was driven a couple of lengths clear away from the last flight.
He tired in the closing stages, however, as Bout Time Bobby stuck on well and had just half a length to spare at the line.
Gateau De Miel had shown improvement last time out at Tramore when chasing home easy winner Brideswell Lad.
O'Keeffe said of his mount: "It's difficult over that trip to keep going out in front the whole way.
"He travelled away and jumped well. At least he came on from his good run the last day, so it is nice to get his head in front.
"He enjoyed that ground and being out in front, so hopefully there might be more to come from him."