Chambard, ridden by Lucy Turner, won the Becher Chase at Aintree.
The 18-1 shot pulled away with two of the 21 fences remaining as Coko Beach finished second and Percussion third.
"He's been incredible," Turner told ITV4. "I wasn't sure if it would be too much of a stamina test for him, with the fences and the ground, but he's been brilliant."
Trainer Venetia Williams said: "She knows that horse so well. It's just so amazing. I'm so thrilled."
Not So Sleepy - like Chambard, an 11-year-old - won the Fighting Fifth Hurdle at Sandown.
Nicky Henderson withdrew current champion hurdler Constitution Hill and stablemate Shishkin from a race that was rescheduled from Newcastle last week and had only four runners.Check out the latest horse racing results