Ed Vaughan's Dame Malliot just touched off Jane Chapple-Hyam's Love So Deep as British raiders dominated the Group Two Darley Prix de Pomone at Deauville.
The two met last month in a Listed race at Newmarket, in which Dame Malliot had more than seven lengths to spare over Love So Deep - but this time it was much closer.
John Egan attempted to make most of the running on Love So Deep, who had subsequently won the Challice Stakes at Newmarket.
While Frankie Dettori seemed confident on the eventual winner, Love So Deep found more inside the final furlong and refused to buckle.
It was not until the final few strides that the advantage began to dwindle - and the pair crossed the line almost locked in unison.
When the result of the photo finish was announced Dame Malliot had got the verdict by the narrowest of margins - which, given the brilliant season Dettori is enjoying, should probably not have come as a surprise.
To complete a clean sweep for the British raiders, William Haggas' Klassique finished third, but Aidan O'Brien's South Sea Pearl was a big disappointment.
Winning trainer Vaughan told Sky Sports Racing: "I was really worried until the result was called. She hated the ground, so I think we've just got away with it. That's only her fourth run. She can only improve because she's still a big, raw filly.
"We had her in a Group Three here last week but couldn't run her. We've won a Group Two now - so we're delighted."
Vaughan can therefore begin planning future targets.
He said: "We were thinking of the Park Hill (at Doncaster), but that's another Group Two. There is a mile-and-six race back here - and she's in the Filly & Mare race at Ascot, but soft ground would be the worry there.
"Hopefully she might stay in training. Anthony Oppenheimer (owner) is a wonderful man to train for."
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