Cooldine, backed down to 9-4 from 9-2, ran out an impressive 16 length winner of the RSA Novices' Chase ahead of Jessica Harrington's 66-1 outsider Horner Woods and Massinis Maguire to earn a 10-1 quote for next year's Gold Cup from William Hill.
Walsh said: "I love this horse. He's a heart as big as a lion and jumped like a stag. He's a hell of a good horse."
Sir Alex Ferguson's What A Friend was under pressure some way from home and faded to finish last.
And the bookies were hit equally as hard in the Ballymore Properties Novices' Hurdle when Walsh and Mikael D'Haguenet justified support from 4-1 into 5-2 by beating Karabak and Tony McCoy by a length and three quarters.
Mullins said: "He has a huge, high action and on better ground today he let his action flow as though he changed his stride. Very few horses can do that.
"Ruby has booked the ride on him over fences. He said that to me already after riding him in Naas. He said this could be a Gold Cup horse." Walsh added: "He's a machine. He had a look at the second last, but when they closed up around him he just came back on the bridle."
The day opened with success for local trainer Nigel Twiston-Davies's Tricky Trickster. The 11-1 shot was winning for the Million In Mind Partnership syndicate.