Boston Bob came late under Ruby Walsh to take the Bibby Financial Services Punchestown Gold Cup from First Lieutenant.
In victory, he completed a transition from nearly-horse to a three-mile leader in less than a month by claiming a second consecutive major Grade One.
Returned briefly to hurdling after his novice chasing campaign took a turn for the worse, the 5/2 favourite had offered a reminder of his capabilities when delivered late in Aintree's Melling Chase and again proved too powerful over a longer distance by galloping three and a quarter lengths clear of the continually-luckless First Lieutenant.
It was further compensation for owner Graham Wylie, who made the gentlemanly decision not to contest the decision of the Cheltenham stewards when On His Own was a controversial runner-up in the Gold Cup, as well as for jockey Ruby Walsh, who was suffering from the agony of a fractured arm at that very moment.
Walsh, now fully recovered, snubbed On His Own for Boston Bob, and Paul Townend took the reins on his Willie Mullins stablemate, who led to around halfway but faded with a whimper.
Lyreen Legend assumed that position, closely tracked by Long Run, who for some way looked as if he might rival the sort of magical comeback made by the veteran Sizing Europe on Tuesday, but still performed commendably to finish third after his fall in the Grand National.
First Lieutenant so often finds a couple too good at this level but first-time blinkers and the help of Barry Geraghty seemed to give him a boost and he was leading at the final fence.
But Walsh had the fire in his belly, surviving an awkward landing over the last and able to drive Boston Bob through, even as his mount seemed at one brief stage to be heading so close to the rail he might have been bound for the stands.
Mullins said: "Boston Bob is just improving. I thought he'd been unlucky twice at Cheltenham (notably when falling in last year's RSA) but he's got his reward for what he shows me at home.
"I was disappointed with On His Own, who needed a bit of company and his jumping went to pieces.
"I'm thinking of the Grand Steeple-Chase de Paris for On His Own and I think we'll bring Boston Bob back next season and aim him for the (Cheltenham) Gold Cup. He has turned the corner now.
"We had mentioned him being a Grand National horse but I think we'll go down the Gold Cup route instead. I suppose we'll enter him for the James Nicholson at Down Royal in November and he could start there next season or in the John Durkan. Any day you can win the Gold Cup here is magic."
Walsh said: "I have to thank Willie. I never thought I'd be siding with On His Own over Boston Bob, but I rode them both the other morning and I was definitely leaning On His Own's way.
"On Monday morning I was talking to Willie and he fairly convinced me to ride this lad, so thanks to him.
"He ducked and I nearly fell off him. He was a bit deliberate at the second-last and wasn't great at the last. He hung left, but he quickened up and won."
Sky Bet responded to the victory by cutting Boston Bob from 20/1 to 12/1 for next season's Cheltenham Gold Cup.
Referring to the Gold Cup, when On His Own was beaten a short head but was denied a clear run by the successful Lord Windermere, Walsh said: "They were so unlucky at Cheltenham, but that's racing.
"The way Graham and Andrea Wylie accepted defeat was admirable in any sort of sport."
Long Run, the former Gold Cup and King George hero, left trainer Nicky Henderson thrilled in finishing a solid third, arguably his best effort of the season.
He said: "It was a good race and I think that was the best round of jumping I've ever seen from him.
"He's even in the Grand Steeplechase at Auteuil and although it's only a few days away, you wouldn't entirely throw that idea away yet. He knows his way around the place.
"You keep bumping into the same people in Grade Ones, but there's no other option.
"The way he jumped and finished, you'd say why not go for the Grand National again next year?"