The former Chelsea boss had not been in charge for the opening two games because of pneumonia.
Cristiano Ronaldo, who scored four goals in his last game for Portugal, endured a frustrating day and saw a late bicycle kick go well off target.
Franck Ribery made his first Serie A start for Fiorentina.
The Bayern Munich legend had an impressive game and forced Wojciech Szczesny into a good first-half save.
Italian champions Juventus, who won their first two matches, lost Douglas Costa, Miralem Pjanic and Danilo through injury.
Fiorentina have not won in 17 league games, with Vincenzo Montella still searching for a first Serie A victory since returning as manager in April.