The French import was slashed to 12-1 from 25-1 for the Triumph Hurdle with Betfair and Paddy Power after adding to an Auteuil success when with Francois Nicolle and a win at Exeter for his new trainer Paul Nicholls.
Monmiral travelled like a 1-2 shot should throughout the extended two-mile journey as Gold Desert made a bold bid to lead all the way.
The race looked over when Monmiral went to the front at the third-last flight, but he gave Gold Desert another chance when fluffing the penultimate obstacle.
However, Monmiral was fluent at the last and drew away on the flat to score by 11 lengths in the hands of Sean Bowen and lift the Grade Two spoils. Glorious Zoff was 22 lengths away in third place.
“He’s a lovely horse. He travelled great. He was probably in front too soon,” said Bowen.
“He was just travelling and winging hurdles.
“He’ll be better with a lead for longer, but I like him a lot.
“He wasn’t great at the second last, but he was just having a look round in front and he was good at the last.
“He’ll keep improving. He’s a very nice young horse.”
Bowen, who had fallen from Billingsley earlier on the card, did not take up his mount, Give Me A Copper, in the concluding bet365 Handicap Chase.
He was signed off by the racecourse medical officer and replaced by amateur rider Angus Cheleda.
Fergal O’Brien reached a personal best of 64 winners in a season when Hurricane Harvey took the Grade Two bet365 December Novices’ Chase at Doncaster.
The Cheltenham-based handler was at the South Yorkshire venue to enjoy the moment rather than attend his local track.
“To get to 64 winners at this time of year is fantastic,” he said.
Hurricane Harvey (5-2) got the better of long-time leader Milanford to land the spoils by a length and a quarter in the hands of Paddy Brennan.
House Island was third with the favourite Ofalltheginjoints tailed off to be a disappointing last of four after never travelling or jumping well.
O’Brien said: “We are starting to grow up a bit because for the last few years we’d have probably ended up at Cheltenham trying to take on better horses there, but this was the right race to go for with him and it’s paid dividends.
“Connor (Brace) gave him a great ride first time and Paddy gave him a lovely ride the second. We got beat by a very good four-year-old (Ga Law) at Wincanton, so we’re delighted.
“He’s won his Grade Two and it’s great for connections. They have been great supporters of mine.
“I’d be lying if I said he was a natural. He takes a bit of work. I’m grateful to Martin Keighley who has a line of five fences. He’s let us go there and we do plenty of jumping with him at home.
“He’s a very honest horse and gets on with the job.”
O’Brien will give Hurricane Harvey’s next race some thought.
“He’ll go on any ground. We did think possibly about Kempton for the Kauto Star, but that just might come a bit soon, so we might put back on the backburner,” he added.
“We’ll enjoy today. There aren’t any people here, but it’s great to come here and we’re grateful.”
Brennan said: “It was his first time over three miles. It’s lovely to come here. He was in at Cheltenham, but three miles on a flat track is right for him and he is only going to improve.
“He’s done us proud. He’s won a Grade Two. We can’t ask for any more.”