La Viola needed the Brazilian to come to their rescue despite appearing on course for a thumping win as goals from Juan Cuadrado, Alberto Aquilani and Adem Ljajic put them 3-0 ahead just after the opening half hour.
Barreto gave the visitors hope just before the interval and strikes from Mario Santana and Alessio Cerci put them back on an even keel, but Romulo ensured their endeavour was not rewarded late on.
To compound their misery, Matteo Darmian was sent off in injury time for a second bookable offence.
Torino are seven points clear of the Serie A drop zone with five games remaining, while Fiorentina are just a point behind AC Milan, who play league leaders Juventus later on Sunday.
The visitors started well and Cerci may have been wishing he had tested Emiliano Viviano after dashing into the box and firing wide had he known what was to come.
Vincenzo Montella's men were ahead as early as the eighth minute when Cuadrado dashed past Mario Santana before delightfully lobbing Torino goalkeeper Jean-Francois Gillet.
The Tuscany club were then two goals to the good in the 16th minute when the unmarked Aquilani headed home from Borja Valero's cross.
The former Liverpool midfielder then fired high over the bar, but it did not seem to matter as Ljaljc put Fiorentina further ahead with a superbly weighted free-kick from just outside the area.
The one-way traffic continued and Gillet had to be at his best to tip away Valero's strike although Torino served notice of their intent when Giuseppe Vives narrowly missed the target from close range.
Fiorentina clearly did not heed the warning and Barreto latched on to Santana's through ball before slotting past Viviano just before half-time.
Clearly buoyed by their goal before the break, Torino came flying out of the traps in the second half and Santana reduced the deficit to just one goal in the 56th minute with a lovely low strike from the edge of the area.
And the comeback seemed complete when Cerci magnificently curled into the top corner from distance in the 77th minute to leave home fans stunned.
To their credit, Fiorentina refused to roll over and on-loan Udinese midfielder Cuadrado was inches away from finding the bottom right corner with his effort.
But Romulo would make no mistake four minutes from time when he collected Mounir El Hamdaoui's through ball before rounding Gillet and rolling into an empty net.
It was such a cruel blow for the defiant visitors but worse was to follow for them when Darmian picked up his second yellow card after fouling Cuadrado in the first minute of injury time.