Imperial Commander stayed-on strongly up the hill for trainer Nigel Twiston-Davies and jockey Paddy Brennan to land the totesport Cheltenham Gold Cup.
The 7-1 chance travelled powerfully all the way and with Kauto Star falling four fences out, only 2008 Gold Cup winner Denman could stay with him on the turn for home.
Imperial Commander was easily travelling the best of the two, however, and after going clear on the run to the last, he powered away on the run-in to win with seven lengths to spare.
In a dramatic race, reigning champion Kauto Star - chasing a hat-trick of Gold Cup successes - made a horrendous mistake at the eighth fence and never really recovered.
Ruby Walsh began to get lower in the saddle a full circuit from home and looked beaten when coming to grief at the fourth-last. Thankfully, he soon rose to his feet.
Fellow Paul Nicholls' inmate Denman travelled with zest towards the head of affairs under Tony McCoy, but Imperial Commander was cantering all over him turning for home.
Denman refused to go down without a fight, but Imperial Commander began to stamp his authority on the run to the last and passed the post with plenty in hand.
Denman filled the runner-up spot for the second year in succession, while last year's Grand National winner Mon Mome (50-1) finished strongly to finish third.
Brennan said: "It's by far the best day of my life. I'm speechless. It was a dream the whole way.
"I've just got to take time to thank my boss (Twiston-Davies). He's the best boss ever - he's produced two horses this week (Imperial Commander and Champion Hurdle runner-up Khyber Kim) and I just had had to steer them."
Twiston-Davies said: "It's absolutely superb.
"I thought Kauto was in trouble some way out before he fell.
"All the hacks (press) were saying he didn't stay so we'll go for the Ryanair next year!
"It's just absolutely brilliant. It's been very hard for us sat there with the third-favourite when all the talk was about Kauto and Denman but we always knew we were going to win."
McCoy said: "When we came down the hill he (Imperial Commander) was going a bit better than me. I hoped he might stop but that's not the way it turned out."
Mon Mome's jockey Aidan Coleman said: "Roll on Aintree. As you expect from a Grand National winner he got outpaced at one stage, but he stayed on great and he has run a super race."
Denman's joint-owner Paul Barber said: "On this ground I was absolutely thrilled with Denman. Let's not forget the best horse won by a long way today and I look forward to taking him on again next year."
Harry Findlay, Denman's other part-owner, said: "Both the Paul's (Nicholls and Barber) are very happy with that. It was a great performance. I thought in running we were going to win it, but Imperial Commander has shown a lot of class and speed and all I can do is take my hat off to him.
"He (Denman) looks a National horse through and through and I'd be very surprised if he doesn't take in next year's race."
Venetia Williams, trainer of the third, said: "I felt a bit funny using a Gold Cup as a prep run for Aintree but I'm so delighted with that run.
"I thought he'd have a chance of getting in the first five but the way he finished up that hill reminded me of being at Aintree last April."