Dusan Vlahovic came off the bench and bagged a brace before the late Federico Chiesa strike, as Fiorentina fought back to knock Monza out of the Coppa Italia.
It was very hard going, as Vincenzo Montella’s men were trailing for most of the match, but go through to the Fourth Round of the Coppa Italia, where they will face Carpi or Cittadella.
The Viola had their first competitive game of the Rocco Commisso era after 17 years under the Della Valle brothers. Cristiano Biraghi was benched amid confirmed negotiations for a transfer to Inter, so 20-year-old Aleksa Terzic started at left-back instead.
Riccardo Sottil forced an early save, then there was a triple chance for the hosts with Federico Chiesa and Kevin-Prince Boateng shots charged down, until Marco Benassi eventually blasted over.
However, it was Serie C outfit Monza who took the lead in front of a stunned Stadio Franchi crowd, Andrea Brighenti turning in a cross from the right.
Monza are run by former Milan pairing Silvio Berlusconi and Adriano Galliani, with ex-Rossoneri Coach Cristian Brocchi on the bench.
Chiesa and Benassi failed to finish off good opportunities as Fiorentina poured forward in the second half, but Boateng’s finish did not live up to the Chiesa solo slalom through defenders.
When Boateng did get the ball in the back of the net on 70 minutes, he was correctly flagged offside on Luca Ranieri’s cross, then substitute Dusan Vahovic was denied from close range by a decisive block.
It was only a warning, as Vlahovic sprung the offside trap on a smart Tofol Montiel through ball and kept his cool to drill into the far bottom corner past the on-rushing goalkeeper. The equaliser came at the 80th minute, just as the crowd were beginning to lose hope.
The two 19-year-olds combined yet again six minutes later to turn the game around, as once more Montiel threaded through a perfectly-weighted pass for Vlahovic to finish from 12 yards. They know each other well from the Primavera youth team.
Monza fell apart and Chiesa sealed it with a solo strike, curling first time into the far bottom corner with his right boot from outside the area.
Fiorentina 3-1 Monza
Brighenti 35 (M), Vlahovic 80, 86 (F), Chiesa 89 (F)
Fiorentina:Dragowski; Lirola (Venuti 48), Milenkovic, Ranieri, Terzic; Badelj, Benassi (Vlahovic 74), Pulgar; Sottil (Montiel 65), Chiesa, Boateng