Arbre De Vie reversed Galway Plate form with stablemate Shaneshill to land the At The Races Chase at Galway.
Shaneshill had filled the runner-up spot in Wednesday's feature event, with Arbre De Vie back in sixth place.
With Ruby Walsh unsurprisingly having stuck with Shaneshill, he was the 4-9 favourite to go one better, with Arbre De Vie 9-4 in the hands of Paul Townend.
Shaneshill cut out much of the running until making a bad blunder five fences from the finish, with Walsh doing miraculously well to keep the partnership intact.
The market leader managed to get back on an even keel, but Arbre De Vie was travelling much the better of the pair rounding the home turn and was pushed out hands and heels by Townend to prevail by six lengths.
Mullins said: "That's a nice race for Arbre De Vie to open his account over fences. He will probably go down the novice route and I'd imagine that Shaneshill will go for the Kerry National.
"Ruby did very well to stay on board Shaneshill, and it was a fair performance by rider and the horse not to fall. He was probably a shade unlucky not to win."