Celtic's Champions League rivals Atalanta were left stunned as former Arsenal and Chelsea man Cesc Fabregas led Como to a first Serie A victory in more than two decades.
Fabregas and his players celebrated in the Gewiss Stadium in Bergamo – where Brendan Rodgers will take his side next month on matchday three of UEFA'spremier competition – after edging a five-goal thriller against the Europa League holders.
And it comes just days after another of the big guns in Celtic's section, Borussia Dortmund, were hammered 5-1 in the Bundesliga with the Germans next up for the Hoops in Europe.
Celtic kicked off their campaign with a 5-1 thrashing of Slovan Bratislava at Parkhead and with confidence soaring through Rodgers' side they will be even more hopeful ahead of two tough away days given their rivals have both stumbled domestically.