Juventus lost 2-0 at Como in Serie A on Sunday, another disappointing result after five successive draws in all competitions for Igor Tudor's side.
Como took the lead in the fourth minute when defender Marc-Oliver Kempf volleyed in from close range at the far post following Nico Paz's curling cross.
Juventus thought they had equalized in the 36th minute when Jonathan David slotted home from close range, but the Canadian's effort was ruled out for offside in the build-up.
Juventus continued to struggle and Paz doubled Como's lead in the 79th minute with a brilliant solo effort, cutting inside from the right to glide past Andrea Cambiaso before curling a left-footed strike beyond Michele Di Gregorio.
The 21-year-old Argentine has contributed to eight of Como's nine league goals this season with four goals and four assists in seven matches, the most in Serie A.
Como moved up to fifth in the standings, level on 12 points with Juventus in sixth. It was the hosts first Serie A win over Juve since 1952.
Fabregas, who led Como to promotion last season, spoke with his former Arsenal coach Arsene Wenger before the match.
"I thank him because at 16 he believed in me, just as I believe in Nico Paz, who is a champion," Fabregas told DAZN.
"I'm very confident about his future because I can recognize when a player has the mindset to become a top player. If he continues like this, he can go wherever he wants."
Juventus began the league season brightly, netting seven times in their first three games, but the goals have dried up since their 4-3 win over Inter Milan last month.
Tudor brought on striker Dusan Vlahovic for midfielder Manuel Locatelli in the 77th minute, two minutes before Paz's goal.
"I don't know who else plays with two strikers (David and Vlahovic) and two wingers, probably only us," Tudor said.
"We believed this setup was the best for the team and I think it was the right choice regardless of the result ... but against a side like Como you have to run a lot.
"We got caught on that counter-attack and at 2-0 the game was over, there was nothing left to do."
