Steadily working his way through the field, the 33-1 shot was sitting a close third as The Last Samuri and Vics Canvas jumped the last together.
The Last Samuri battled on at the elbow but could not quite hold off the strong-finishing Mouse Morris-trained nine-year-old, who was remarkably winning for the first time over fences.
Forging on inside the final 100 yards under 19-year-old David Mullins - on his first ride in the race - the Gigginstown House Stud-owned gelding eventually crossed the line six lengths ahead of 8-1 joint-favourite The Last Samuri.
Vics Canvas was third at 100-1 and Gilgamboa (28-1) fourth.
Mullins said: "It's unbelievable. I just couldn't expect things to have gone better. There was one little mishap at the fourth-last, but thank god I came out (the other side). Everything went to plan really.
"Credit to Mouse, he's produced this horse without having won over fences. Then there's me, who's never even walked around the Grand National track.
"Mouse is a genius and he's the best man in the world for preparing a horse for one day. I'm very thankful to Michael and Eddie O'Leary (of Gigginstown) for giving me the chance.
"That's the best ride I've ever got off a horse and it's the best feeling to come back into a place like this. It was just brilliant."
Morris was almost lost for words after the race, but paid tribute to his late son, Christopher, who tragically died last summer from suspected carbon monoxide poisoning while travelling in South America.
Having also won the Irish National on Easter Monday with Rogue Angel, Morris said: "I don't know what to say. To have the two in a couple of weeks is unbelievable. I've a lad who's doing overtime for me up above."
Morris has never made any secret of the regard in which he holds Rule The World, who has suffered his fair share of injury problems.
He said: "It's Disneyland - fairytale stuff. He's fractured his pelvis twice. Before that I always thought he was the best horse I ever had, how good would he be with a proper rear end on him?
"He had a nice weight and he's a class horse on his day. I know he was a maiden (over fences), but he's been running good races - Grade One races - and banging on the door. This is next best to the Gold Cup (won with War Of Attrition in 2006)."
Gigginstown supremo Michael O'Leary also won the Gold Cup at Cheltenham last month with Don Cossack and said: "This is the cream on top. I don't know what to feel, I'm numb. I thought I had no chance in it, I wanted to win a Gold Cup and it was beyond dreams that I could win a Grand National.
"To win a Gold Cup, Irish National and Grand National in one year - I think I should stop, it's not going to get any better than this."
Douvan delivers again in
Douvan proved a class above his rivals to follow up his impressive Arkle success with an equally stylish victory in the Doom Bar Maghull Novices' Chase at Aintree.
Although his jumping was far from perfect over the first three fences, the 2-13 favourite quickly warmed to the task before disposing of his rivals with the minimum of fuss.
Tracking Alisier D'Irlande throughout the two-mile event, the six-year-old breezed past with a slick jump over the fourth-last. As the long-time leader wilted, it was left to The Game Changer to go off in pursuit of the Willie Mullins-trained machine, but it was a task that proved impossible.
Finding another gear on the run down to the final fence, the Rich Ricci-owned winner saved his best until last, producing a superb leap before cantering away in effortless fashion to score by 14 lengths, completing a quickfire double for Mullins and jockey Paul Townend after striking with Yorkhill earlier on the card.
Townend said: "That was some experience. I was doing a half-speed everywhere.
"He had a little look between the last two (fences), I gave him a squeeze and I've never felt anything pick up like it. I had so much horse underneath me.
"It's unbelievable the firepower Willie Mullins has and I'm very fortunate to be in the position I am, to step in when Ruby (Walsh) had the misfortune like he had yesterday.
"He has so much natural ability and for a big horse he's very clever. He's a gent to do anything with at home - he's a big, friendly giant.
"He covers so much ground and does everything so easy. He's a proper horse."
Mullins said: "I wasn't happy with his jumping early, but that's probably because he was travelling too easy. He wasn't clean enough (at his fences) until Paul sent him on.
"It was hard on Paul riding him for the first time in a race like this. Knowing that there was a front-runner that was likely to go on, Paul had to balance it, but he got it right. Paul said he couldn't believe how much he lengthened when he let out an inch of rein.
"I've told everyone before that I've never seen a horse like him on the gallops. He's never been off the bridle.
"I'd love to go to Punchestown with him, but we'll just have to see. It might not be fair on the horse. Everything is open. He could step up in trip next year."
Yorkhill digs deep
Yorkhill maintained his unbeaten record over hurdles to complete a Grade One hat-trick with a workmanlike success in the EZ Trader Mersey Novices' Hurdle at Aintree.
Having posted one of the standout performances at last month's Cheltenham Festival when winning the Neptune Investment Management Novices' Hurdle, the six-year-old produced a display of completely different contrast before mastering his rivals in the two-and-a-half-mile contest.