Sloan Privat's extra-time strike was enough to seal 1-0 win over Gazelec Ajaccio on Wednesday and send Guingamp into the last 16 of the Coupe de la Ligue.
The 26-year old was on hand at the end of the first period of extra time, producing a calm finish to finally break a stubborn home rearguard and send his side through.
Heavy rain provided difficult conditions at the Stade Ange Casanova in a tie that had previously been called off in October due to a water-logged pitch.
John Tshibumbu tested visiting goalkeeper Jonas Lossi with a 15th-minute header, before Lauren Dos Santos responded by sending a low 20-yard drive narrowly wide.
Privat should have found the net in the final 10 minutes, while Mana Dembele's late effort was ruled out for offside.
Dembele planted a header straight into the arms of goalkeeper Jules Goda early on in extra time, before Privat finally broke the deadlock in the 103rd minute and put his side into the next round.
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