Despite Fiorentina's second half rally, which saw them come back from 4-1 down, Sassuolo held on to move out of the relegation zone. Berardi took his goal tally to 16 for the season and the 19-year-old staked a late claim for a World Cup place. Fiorentina failed to wrap up fourth place as their hangover from Saturday's Coppa Italia final continued.
Antonio Rosati was given his Serie A debut between the home sticks due to Norberto Neto being sidelined with a fractured finger. Viola boss Vincenzo Montella rotated his squad in the wake of Saturday's defeat. Juan Cuadrado was back after being suspended for the final, while Modibo Diakite, Alessandro Matri and Rafal Wolski also came in to start. Giuseppe Rossi was back on the bench after four months out with a knee injury, but Mario Gomez was in the stands after being ruled out for the rest of the season.
Sassuolo travelled without the suspended Francesco Magnanelli, but welcomed Berardi, Simone Missiroli and Davide Biondini back from bans.
Fiorentina had the best of the opening minutes. Borja Valero curled a free kick beyond Wolski stretching in at the far post, before Mati Fernandez's effort ricocheted off Cuadrado and finished wide.
Rosati kept out Nicola Sansone on 15 minutes, after the attacker dribbled past defenders and scuffed a shot towards goal. Diakite's pull back was wasted by Fernandez, who took too long to pull the trigger. Gianluca Pegolo got down low to save a weak shot from Cuadrado.
Sassuolo had started with three in attack and remained dangerous going forward. Gonzalo Rodriguez adjusted his body to intercept Berardi's pull back before it could reach an unmarked Sansone. Simone Zaza was denied at the near post by Rosati, who then had to stretch himself to tip over a Marcello Gazzola rocket.
The visitors were awarded a penalty midway through the first half. Sansone drew Rosati out of his goal and Biondini saw his shot charged down by Valero right in front of the referee. Berardi stepped up and sent Rosati the wrong way.
Fiorentina looked for a quick equaliser. Matri glanced a header wide and Cuadrado got in behind the defence, only to have his finishing let him down. Stefan Savic ventured forward to head over from Valero.
The Neroverdi soaked up the pressure and doubled their lead just past the half hour. Sansone found acres of space and his square pass between two defenders found Berardi. The on loan Juventus forward hit a first time shot which squirmed under Rosati's body and rolled into the net.
Fiorentina were shell shocked and Zaza struck the outside of the post with a thunderous shot from distance. Berardi completed his hat trick three minutes before the break. Zaza dispossessed Rodriguez and laid off for Berardi to round Savic and place a shot into the far bottom corner.
Zaza wasted a chance to make it four early in the second half, curling inches over the bar from a promising position. Joaquin Sanchez was brought on by Montella and made an instant impact, winning a penalty after being tripped by Alessandro Longhi. Fernandez stepped up and sent Pegolo the wrong way to give La Viola hope.
The home side had no option but to push forward, which naturally left gaps at the back. Sassuolo exposed that space on the hour when Berardi put the ball on a plate for Zaza to somehow screw wide from six yards. Moments later, Berardi once again found space out wide. This time, Sansone got on the end of the pass to beat three defenders and send a shot in off the post.
Rossi was brought on and took just seven minutes to find the net. The Italian striker played a return pass with Valero, before sending a low shot past Pegolo. Amazingly, Cuadrado pulled another goal back three minutes later. The Colombian ran onto a long ball and lifted it over the onrushing Pegolo. Cuadrado picked up a knock in the process and briefly left the field to get strapping applied to his knee.
Fiorentina laid siege to the Sassuolo goal during a tense finale. Rodriguez couldn't keep his header down from a Manuel Pasqual cross.
There was drama in the final minute when Berardi went down with cramp and didn't take too kindly to Pasqual trying to pull him off the pitch. Both benches spilled out onto the field and Sassuolo were forced to play out six minutes of stoppage time a man down due to Berardi needing treatment.
Deep in stoppages, Pegolo was at full stretch to prevent Rossi deftly touching in Pasqual's cross. Valero thought he had headed in an equaliser at the death, but an offside flag came to Sassuolo's rescue. Replays showed the referee made the right call and the visitors held on for a huge three points.
Fiorentina: Rosati; Diakitè, (Tomovic 70) Savic, Rodriguez, Pasqual; Mati Fernandez, Pizarro, Borja Valero; Cuadrado, Matri, (Rossi 65) Wolski (Joaquin 55)
Goals: Rodriguez pen 57, Rossi 72, Cuadrado 75
Sassuolo: Pegolo; Gazzola, Antei, Cannavaro, Longhi; Chibsah, Missiroli, (Brighi 85) Biondini; Berardi, Zaza, (Floccari 74) Sansone (Ziegler 80)
Goals: Berardi pen 23, 33, 42, Sansone 64