Colin Tizzard's Ryanair Chase hero had only run over three miles once before, in last season's King George where he made mistakes in heavy ground having been held up towards the rear.
Regular rider Joe Tizzard elected to send Cue Card to the head of affairs this time and he was always jumping and travelling well.
Last year's winner Silviniaco Conti looked a big danger three from home, as did Dynaste, but Tizzard had still not asked for everything and after jumping the last Cue Card (9-1) sprinted clear to win by four-and-a-half lengths from Dynaste.
The big disappointment of the race was the Gold Cup winner Bobs Worth, who dropped away tamely.
Colin Tizzard said: "It's almost brought a tear to my eye. Joe was really coy until about three out, he just sat there and never moved. He jumped better than he ever has. He was on his game today, that's for sure."
"It would have been easier staying over two miles as that is where his form was and we were looking at Ascot today with two runners thinking 'why are we here', but this proves he does stay."
"It's everybody's dream to have a horse good enough to run in the Gold Cup and I'm sure unless we get beat by stayers next time that will be on his compass. Everyone says Champion Bumper horses will be three milers but because he has so much pace we've never done it."
Joe Tizzard said: "He was brilliant today, he was a different horse from Exeter (third in Haldon Gold Cup), he was bang on the money and proved what he is. He finds things so easy, he's brilliant to ride, the pace he's got is lovely in a race like this, we've been running him over the wrong trip!"
"He's got that gear which all the best horses have, it's so nice he's proved he gets the trip and it makes him a real Gold Cup horse."
Cue Card has, unsurprisingly, jumped to the head of the King George market, now trading as the 4.1 favourite. Dynaste is the 5.59/2 second favourite.
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