Ridden by Hollie Doyle, Mo Celita made all of the running in the six-furlong event and stayed on well under pressure to cross the line three-quarters of a length ahead of the runner up.
The victory is the latest step in Mo Celita’s rise from a 62-rated participant in selling races to black-type performer, a transformation that began when she joined Nicholls’ yard in April.
Beginning her career on English turf with a hat-trick of wins in sellers, the bay then won twice more after turning her hand to handicapping and ran with credit when beaten by just a length in the Palace Of Holyroodhouse Stakes at Royal Ascot.
A step up to Group Three company in the Summer Stakes at York resulted in a below-par performance, but the three-year-old was out of sorts on that occasion and proved her class at stakes level at Deauville.
The victory is a first Listed winner for Nicholls, who trains just 20 horses in Thirsk, North Yorkshire and has already surpassed last season’s total number of victories.
“She’s a superstar, it was unbelievable,’’ he said.
“We’re only a very small yard with 20 horses and that’s us into double figures (for winners this season), so to win a stakes race on Prix Maurice de Gheest day is unbelievable.
“It’s great for her connections. They bought her for that reason and they could have probably taken her to a bigger trainer, but they stayed loyal and it’s great that she’s repaid them.
“Hollie gave her a great ride, it was just a good result all round.
“That’s our first Listed winner, we came close last year but it’s hard for anybody to get the ammunition.
“It’s great that she’s come up through the ranks. She’s still progressive and she’s only run one below-par race for us at York and she wasn’t right after that when she got home.’’
Mo Celita is jointly owned by David Howden and David Redvers, racing manager for Qatar Racing and owner of Tweenhills Stud, and Nicholls will consult both parties as he plans a next outing for their filly.
“The owners are very professional people and they know what they’re doing, it was the plan to go there and it all worked out - the prize-money is good in France, too,’’ he said.
“There are a few races back in France and there’s a race at the Ayr Western Meeting, there are a lot of options for her.
“She’s got a hell of a lot of speed so coming back to five furlongs is not an issue, so between me and Mr Redvers’ team we’re trying to chart the best course.’’
The Group One Prix de l’Abbaye at ParisLongchamp could be a longer-term target.
“ I think the Prix de l’Abbaye at the end of the year might be an option because she clearly goes on very soft ground, but there’ll probably be a Listed race or a Group Three en route,’’ he said.