Native River won a thrilling Cheltenham Gold Cup after an epic duel with Might Bite.
The 5-1 chance gave Dorset trainer Colin Tizzard his first victory in the race after some spectacular jumping under champion jockey Richard Johnson.
Favourite Might Bite (4-1), seeking a historic Cheltenham Festival treble for trainer Nicky Henderson, was a gallant runner-up, beaten by four and a half lengths.
Anibale Fly (33-1) finished third ahead of Road To Respect and Djakadam.
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But the race was all about the memorable battle between last year's third-placed horse Native River and King George VI Chase winner Might Bite.
The pair led from the front, roared on by a sell-out 70,000 crowd, and went toe-to-toe over 22 fences and three and a quarter miles in soft ground, with none of their rivals posing a serious challenge.
Henderson was bidding to be the first trainer to win the Champion Hurdle, Champion Chase and Gold Cup at one Cheltenham Festival meeting.
And Might Bite looked a serious contender for much of the race, before the 2016 Welsh National winner Native River stormed up the hill.
Johnson smiled broadly after his second Gold Cup win, 18 years after his first on Looks Like Trouble. He was, however, punished for misuse of the whip during the showpiece race - and was handed a seven-day ban and a fine of £6,550.
Victory sealed a 203-1 double for Tizzard, who also works as a dairy farmer, after 33-1 shot Kilbricken Storm won the Albert Bartlett Novices' Hurdle.
Stamina, bravery & tenacity win the day - analysis
BBC racing correspondent Cornelius Lysaght
"It was a terrific performance by both Native River and Might Bite to completely dominate; shutting out the others who never got in with a serious shout.
"At the end, the stamina of the brave and relentless winner lasted out better than the second, who'd loomed up looking likely to win at the second-last. Supporters will doubtless fancy a rematch in less testing conditions.
"It was a spectacular result for all concerned, and for British jump racing, which had been licking its wounds after an often disappointing week dominated by the Irish; the 'Big Three' trophies - the Champion Hurdle, the Champion Chase and the Gold Cup - all stay at home."
'It means everything to me' - reaction
Winning trainer Colin Tizzard, speaking to BBC Radio 5 live immediately after the race: "It was unreal, wasn't it? To win the Cheltenham Gold Cup means everything to everyone's life. Let's not pretend it's not.
"Richard Johnson galloped and jumped as fast as he could and the horse never let him down once. He just powered away.
"We've had a wonderful preparation and you think something could go wrong in the race, but it didn't.
"The Irish have been winning everything this week but Richard gave it that sort of ride. When Might Bite came beside him, Native River just flew over the last.
"He wasn't quite right after Cheltenham last year so we've stuck to the plan and it has come in.
"I never thought in my biggest dreams that I would win a Gold Cup."
Winning jockey Richard Johnson: "The horse jumped great, he answered every question I asked. He's so genuine and the Tizzards gave him a chance and full credit to them. You couldn't ask for a better partner.
"I was lucky enough to win this race 18 years ago and I'm just making sure I'm enjoying this moment as much as possible."
Elliott's success continues - round-up
Irish-trained horses, particularly the powerful stables of Gordon Elliott and Willie Mullins, have dominated the meeting.
And Elliott took the opening Triumph Hurdle with Farclas for his seventh winner of the week, and a fourth for 18-year-old jockey Jack Kennedy.
Elliott's tally was extended to eight when Blow By Blow, ridden by Donagh Meyler, crossed the line first in the Martin Pipe Conditional Jockeys' Handicap Hurdle.
An eighth winner at the Festival equals Mullins' all-time record. There were 17 Irish-trained winners at the Festival and 11 for Great Britain.
Bridget Andrews was a surprise winner of the County Hurdle when she rode 33-1 shot Mohaayed to victory for trainer Dan Skelton.
But there was some sad news when Sandsend, ridden by Katie Walsh, had to be put down after suffering a leg injury during the race.
Three horses - Dresden, Some Plan and North Hill Harvey - also suffered fatal injuries in the concluding Grand Annual Chase.
The final contest was won by Le Prezien under Barry Geraghty to complete a 220-1 double for trainer Paul Nicholls.
Nicholls had earlier taken the Foxhunter Chase for the second year running with Pacha Du Polder.
Jockey Harriet Tucker defied the pain of a dislocated shoulder to win, and become the 14th female jockey to register a victory at the Festival.