Bruno Genesio’s visitors dominated much of the play at the Stade Michel d’Ornano, but Ivorian midfielder Diomande climbed highest to flick a 77th-minute free-kick from Stef Peeters into the far corner.
It is the first time that top-flight side Caen have reached the semi-finals in their 105-year history, and they’ll host PSG, who are bidding for a fourth straight Cup title, in April.
The path appears clear for runaway Ligue 1 leaders PSG to claim a record-extending 12th French Cup after their last-eight victory over Marseille on Wednesday, with struggling third-tier outfits Les Herbiers and Chambly to face off in the other semi-final.
Les Herbiers, playing in only their third-ever season in the third-division Championnat National, edged out Lens on penalties on Tuesday, before Chambly stunned Ligue 1 club Strasbourg 1-0.
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