Watch a full replay of the Ladbrokes Trophy, analysis plus an interview with Joe Tizzard..
The 10-year-old was sent off a 12-1 shot, despite resuming with an 11-length victory at Fontwell in October, and he defied those odds to storm home by 10 lengths this time from better-fancied stablemate Elegant Escape.
Tom Scudamore had Sizing Tennessee in control by the last, having moved into a share of the lead with Dingo Dollar four out in a race run throughout at a hectic pace despite testing conditions.
Alan King's six-year-old eventually stayed on to finish third, a further seven lengths back.
An emotional Scudamore said: "I lost my grandfather two weeks ago, it was his funeral yesterday and I wasn't able to go - those are the sacrifices you make. I was so sorry not to be there, but he was with us today."
He added of the winner: "I was always confident in him, his novice chase form last season was very good and his Fontwell run has turned out well.
"I thought he was under the radar - I didn't expect to win like that, but a win is a win.
"I was always very happy and it was a great thrill."
Tizzard, winning the race for the second time after Native River in 2016, said: "Tom encouraged me when we legged him up as he said he is one of the best handicappers in the race. Sometimes you get lucky. He bolted up first time and we left him six weeks to come to this race.
"He had leg trouble before he came to me and had low mileage. He just strolled away with it. I thought he might run a big race, but to win like that does surprise you. He was the one that unless he clobbered one was going to win.
"He is in the Welsh National and so is Elegant Escape and he has run a real solid staying race. West Approach was there for a long time as well. Three in the first five is almost unthinkable.
"I've always said I'm quite good at training big, slow horses. If the entries went in tomorrow we would enter him in the Gold Cup, as he hasn't done too bad."
He added: "I suppose this our Gold Cup today and it is fantastic for him. I'm sure we could leave him five or six weeks and have a go at something big again."
John Romans, owner of Elegant Escape, said: "We are thrilled with that. It has been won by the yard. I'm thrilled for the Tizzard team and we are one big family. If you are going to be beaten, it is better to be beaten by your main trainer.
"They are talking about the Welsh National. Whether that is the right thing or not, I don't know, or we could keep him for Cheltenham, possibly the Cotswold Chase.
"He likes the soft ground."
King was proud of Dingo Dollar's proud effort.
He said: "It was a hell of run. The rain wasn't ideal. He has jumped superbly and travelled well, so I am very proud of him.
"I was worried, as he never got left alone down the back and Dicky (Richard Johnson on Thomas Patrick) hassled him all the way. The winner has won very well and that may have cost us second.
"We will work back from the Scottish National."
Thomas Patrick was sent off the 3-1 favourite, but was pulled up three out.
Trainer Tom Lacey said: "Obviously it is very disappointing. Whether he wants ground that deep, I'm not sure, as I don't think it was quite that soft at Aintree.
"Richard Johnson just said he felt a bit flat. We will regroup and go from there. Any horse can put in a bad run. He is only a six-year-old, so there is no rush to get him back.
"There will be plenty of options for him." "I was always very happy and it was a great thrill."