Nicolo Fagioli should have given Fiorentina the lead with 10 minutes on the clock when he latched onto a flicked pass and advanced into the area, where he skipped past his man before seeing a close-range effort deflected for a corner.
After this early scare, Como grew into the contest and created three good chances, with Anastasios Douvikas’ header saved at point-blank range by David de Gea before Mattia Liberali shot wide on the rebound and Nico Paz’s close-range header was denied by De Gea.
However, just after the half-hour mark the visitors hit the front when Liberali’s left-footed effort from inside the area beat De Gea and found the far corner of the net.
Things went from bad to worse for the hosts four minutes later when Paz’s header found the left corner, yet they managed to halve the deficit when Marin Pongracic powered the ball home on the rebound from close range.
Pongracic thought he had scored his second goal in four minutes to equalise for Fiorentina in added time, but after a lengthy VAR check the goal was ruled out for offside.
Fiorentina will have hoped to take some momentum into the start of the second half, but they found themselves two goals behind for the second time 12 minutes after the restart.
Douvikas received the ball 25 yards from goal and went past Radu Dragusin to create space for a right-footed effort that went between the legs of the despairing De Gea.
The Greek striker is something of an away specialist, with his last five league goals having all come on the road.
The Viola created a couple of opportunities in the closing stages, with Alieu Njie and Fagioli both testing Jean Butez, but unlike their visitors, Fiorentina’s clinical touch deserted them as they slipped to successive defeats in Serie A.
Como have now won six of their last eight away league matches, with Cesc Fabregas’ men climbing into the top four. Meanwhile, Fiorentina drop to 19th, having now collected fewer than five points after seven Serie A games for just the third time in the modern era.