The 16-time champion jockey Tony McCoy produced an exceptional ride to win the Betfred Cheltenham Gold Cup on Synchronised (8-1).
The Jonjo O'Neill-trained, JP McManus-owned nine-year-old wasn't travelling well at any stage in the contest but he stayed on best of all to catch the 50-1 outsider The Giant Bolster on the run-in.
Long Run (7-4 favourite) was always well placed under Sam Waley-Cohen but he was outbattled up the hill by the first two.
Two-time champion Kauto Star was pulled up on the first circuit with the crowd breaking out in spontaneous applause during the contest.
McCoy said: "It's great for Jonjo and JP McManus.
"He's really delivered today.
"He was off the bridle the whole way and when I missed the third-last I thought my chance had gone."
McCoy, who was securing his second Gold Cup victory after Mr Mulligan struck in 1997, added: "He's an amazing horse and it was an amazing performance.
"I'm so pleased to win it for JP as he's been so good to me.
"Jonjo has done an incredible job. I've got a Grand National and a Gold Cup out of the man and I love
him to bits.
"Jackdaws Castle looks a closed shop with JP and just a few other owners and I can't understand why he doesn't get more horses."
Trainer Paul Nicholls said Kauto Star, whose participation in the Gold Cup was in jeopardy following a schooling fall a fortnight ago, had returned from the race unscathed.
He said: "He's absolutely fine.
"Ruby wasn't happy after he'd jumped a couple of fences and we said if he wasn't happy to pull him up, and he's done the right thing.
"There's obviously something tweaking him."
Midnight Chase set out to make all of the running and initiated a strong pace, with Kauto Star and Long Run close up.
There was drama at the second fence when What A Friend, part-owned by Sir Alex Ferguson, fell.
Soon after it became evident Walsh was not happy with Kauto Star and pulled him up.
Time For Rupert got the better of Midnight Chase before four out, but he was soon swamped.
The Giant Bolster then looked like landing a major shock as he took the lead on the turn for home.
Long Run was in the front rank, but Sam Waley-Cohen was hard at work on him and he failed to show the same acceleration that won the race 12 months ago.
Burton Port also tried to close, but it was Synchronised who was delivered to perfection by McCoy as his stamina proved crucial.
David Bridgwater said of runner-up The Giant Bolster: "He was brilliant, but I've always said this is an exceptionally good horse and he should have been about 16-1, not 50s.
"He jumped super, and it was a wonderful race.
"Hopefully we'll be back here next year and hopefully there'll be some big race to win before then."
Nicky Henderson said of the defeated champion, Long Run, and fourth-placed Burton Port: "I'm thrilled with my two boys and I have to give credit to the winners.
"JP is one of the stalwarts of National Hunt racing and Jonjo and AP are superstars.
"You have to say Long Run was not quite good enough on the day - he was always struggling to get to the pacemakers, but Sam (Waley-Cohen) rode a great race.
"I'd imagine they'll both got to Aintree, the three-mile race (Betfred Bowl) would be good for Long Run.
"I don't know about Burton Port, I'll have to talk to Trevor (Hemmings, owner) but you'd say there's no reason why he wouldn't go to the National as it's the only chance he'll get to run off 11st 7lb."
Sam Waley-Cohen added: "I'm very disappointed he didn't win, but I'm not disappointed in the horse - he's run all right.
"When landing over the last I thought his stamina might see it out, but it didn't."
McManus had never before won a Gold Cup, and was understandably jubilant. He said: "It's a very special day, a very special moment - for Jonjo, for AP and for their families.
"It gives everybody a great lift and I just feel very, very proud."
Walsh said of Kauto Star: "I jumped the water and I wasn't happy at that stage.
"When Kauto Star couldn't lay up with Midnight Chase, I knew I was in trouble.
"I just went further and further back and I was struggling badly going to the fourth-last.
"If horses could talk it would be a lot easier as they could tell you how they were feeling.
"If that was the case, half the horse I've ridden this week wouldn't have run."