Captain Conan made hard work of landing the odds in the Betfred Mobile Lotto Challengers Novices' Chase.
The 1-2 favourite, trained by Nicky Henderson, looked cooked when Third Intention jumped the final fence with a healthy advantage in the Grade One better known as the Scilly Isles.
However, Colin Tizzard's runner found the Sandown hill too much as Barry Geraghty seized the opportunity to galvanise Captain Conan and win by a neck.
"It was definitely harder work than we thought. He jumped nicely, but I knew from the water jump it was going to be hard work," Geraghty told Channel 4 Racing.
"I know Nicky has got an indoor school which has kept them on the go, but I'd say he just lacked a bit of race fitness.
"I don't think the ground was an issue. He's a big horse who wants a lot of work.
"I would say two and a half miles is perfect for him."