Trained by Scudamore's brother Michael, the eight-year-old made most of the running and was clearly enjoying the change of scenery, although he looked a sitting duck as the field came back on to the racecourse proper, with two Emmanuel Clayeux-trained runners chasing him.
As the 14-1 winner crossed the line three-quarters of a length clear of Vicomte Du Seuil, his rider saluted the crowd and said: "To win it for my brother and the owners, who are my sponsors, is great.
"I don't normally ride in these races as I don't really like them, but I enjoyed that!"
Michael Scudamore said: "It's one of those bizarre races, it's something different.
"He took to it at the Festival and he'd been going well at home, but things haven't been going so well of late so that's great.
"He'll probably come back here for the race in December and he could creep into the National, which would be the dream."
Exitas was chasing a hat-trick going into the race and moved menacingly into contention, but the 3-1 favourite had challengers on either side.
Henderson said: "Everyone kept saying who do you think will win? The other horse had been and done it and this horse was open to improvement.
"Paddy said when he ran here last time it was just too quick and he couldn't cope jumping-wise, but today was just right.
"Paddy always said there'd be a nice race in this horse, he's a good strong horse and last year he won five for us, he just needs the right ground.
"We bought him as a three-mile chaser, but clearly he's a two-miler. He might get two and a half, but clearly he's all speed."