Mags Mullins' eight-year-old does not have too much chasing experience under his belt but was given a patient ride by Danny Mullins and crept gradually into contention.
A Sizing Network gave up the lead he held since flagfall when Arkwrisht headed him two out, but Logical Song came there pulling double.
Once Mullins pressed the button, the 7-1 chance strode clear and crossed the line with 12 lengths in hand.
Raz De Maree, a dual winner of this race, produced another honourable effort for second, with Undressed third and Arkwrisht fourth.
Mags Mullins said: "Danny was anxious to step up to three and a half miles and even Daniel (Furini, owner), in Italy, was wondering was it too far for him, but I said we'd ride him to get it (the trip) and see.
"He is so honest and is so genuine and I'm delighted with him and he jumped super.
"He always just stays and over a shorter trip something with more gears would get him but he is great and has given us great fun.
"I'm delighted to win a National and it opens up options now."
Bamako Moriviere was a fine winner of the Grade Three novices' chase on the card.
Willie Mullins' six-year-old was much too good for Jury Duty and ended up claiming victory by 16 lengths in the hands of Ruby Walsh.
Walsh said: "He had plenty experience and had a win over two miles and was in against Jury Duty, who lacked experience.
"He pinged the third-last and quickened up really well and put the race to bed there."
Cracking Smart (5-4 favourite) won a third race on the bounce in the Listed novice hurdle over three miles.
Gordon Elliott's five-year-old was not foot-perfect, but he did not need to engage overdrive to account for Robin Des Foret by eight and a half lengths.
Assistant trainer Davy Condon said: "Whatever he does this year will be a bonus because he is a real chaser for next year.
"Like all horses Eddie (O'Leary) buys for Gigginstown he'll have natural progression over hurdles and is your ideal model for chasing.
"I doubt Gordon will overdo him over hurdles this year and will mind him away but is one to look forward to."