Diamond Necklace (4/5 favourite) won the Emirates Poule d'Essai Des Pouliches at ParisLonghcamp for Aidan O'Brien and Ryan Moore.
Last seen winning the Prix Marcel Boussac here in October, Diamond Necklace jumped well for Moore and raced in a share of fourth behind early pacesetters Zanthos and Isle Of Fernandez.
In a repeat of the colt's classic, Moore kicked at the cutaway at the top of the home straight and made smooth progress to hit the front towards the inside.
From there it was just a case of keeping Diamond Necklace up to her work and she ran on well in the ever worsening conditions to win comfortably from The Last Dance and Green Spirit by three lengths and a length and a half.
It was O'Brien's first victory in the Pouliches since Rose Gypsy in 2001 and the delighted trainer told Sky Sports Racing: "Everybody at home has done a lot of work with this filly and Ryan gave her a brilliant ride.
"She's like her dad [St Mark's Basilica], improved from two to three. Last year she was very classy, Christophe [Soumillon] won on her twice. First time for Ryan to ride her on a raceday and gave her a beautiful ride. What can you say? She's got a lot of natural ability and over the moon for everybody.
"She's a lovely filly, very natural. I didn't get to speak to Ryan about how far she'd stay but she went through the race very easy, handled the ground very well and she's just a natural and her dad was like that. He won the Guineas and went back and won the French Derby and we saw what he did after that.
"She's beautiful. She's all her dad and he improved a lot from two to three and she looks like doing exactly the same.
"We had it in our heads that she would be a Prix de Diane filly or the Oaks, it will depend on what the lads want to do. She's very exciting and we're so lucky to have her."
Moore, when asked whether Diamond Necklace would stay 10 furlongs, simply replied 'we haven't had the discussion yet'.
The leading jockey went on: "She quickened up very well, got to the front very early and was just doing enough then. Obviously a high class filly with a good turn of foot that St Mark's Basilica had himself and that's probably what separates them.
"She gives that indication [of staying 10 furlongs] but she's very comfortable at that pace as well so we'll see."
Diamond Necklace was cut to a general 2/1 (from 11/4) for the Prix de Diane and is now 5/1 with Paddy Power and Sky Bet for the Oaks at Epsom, behind only stablemate Amelia Earhart who is the 11/4 favourite.
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