Guingamp came from behind to draw 2-2 with 10-man Monaco before clinching a dramatic victory on penalties in Tuesday's Coupe de la Ligue semi-final, as Leonardo Jardim endured a disappointing return to the Principality club.
Monaco, who appointed Jardim for his second spell as coach after sacking Thierry Henry on Friday, raced into a 2-0 lead despite having loanee midfielder William Vainqueur sent off.
Rony Lopes and Aleksandr Golovin found the net for the visitors but Guingamp improved dramatically in the second half and levelled through Alexandre Mendy and Marcus Thuram.
Marcus Coco held his nerve to score the winning penalty for Guingamp as Monaco's nightmare season continues, and Jardim must now pick his players up before they face Toulouse in Ligue 1 on Saturday.