15/8 favourite Long Run registered a remarkable victory in the William Hill King George VI Chase at Kempton.
Sam Waley-Cohen looked set for a comfortable win aboard Nicky Henderson's charge when setting sail for home after the third last but the seven-year-old began to wander in front.
Seeing an opportunity, Richard Johnson conjured a sustained charge from Captain Chris and when more fluent than his rival at the last, he jumped to the front.
However Long Run was galvanised for another effort and he was back in front two strides from the post. Grands Crus (7/1) was back in third.
The winning rider said: "He was so brave, we wanted to take the sting out of everything else and I asked so much, but he was so brave. That was racing at its best to my mind, that's why we do it. I can't put it into words - it's an honour and a pleasure."
Long Run is owned by Waley-Cohen's father Robert, who added: "He's come here four times now and won three Grade Ones and been second to Kauto Star.
"I wasn't absolutely sure that we had got back up but as I came down the stairs from the stand, I saw his name go up and that was fantastic."
Henderson was similarly thrilled to see his former Cheltenham Gold Cup victor return to winning form.
He said: "It was a brave call to go on when he did and it was the right call to make.
"It was a battle out there today and not the best ground for any of them. He's young but has been doing everything right.
"You would have to say last year was a disappointment but he's been running good races all the time."