The hosts started badly as Marash Kumbulla saw red, while Armand Laurienté ran riot.
Credit to Jose Mourinho’s men, who never stopped fighting but missed an opportunity to catch Inter in second place.
Coincidentally, this happened when Jose Mourinho started his two-match ban that prompted a ‘pañolada’ protest from the crowd – waving white handkerchiefs.
The Neroverdi came to Italy’s capital on four wins from their last six games.
The first chance came to Roma in the opening minutes when Gini Wijnaldum fired straight at Andrea Consigli after springing the offside trap, while Tammy Abraham’s chest and volley bobbled wide.
However, Sassuolo drew the first blood with their first real foray forward. Edoardo Bove failed to control a wayward Stephan El Shaarawy pass in midfield to spark a counter-attack.
Smalling tried defending by throwing himself in the way of Davide Frattesi’s strike, then Rui Patricio got a glove to the Andrea Pinamonti follow-up, but the hosts were helpless with Armand Laurienté tap-in.
After conceding the first goal at home in 202bu, Sassuolo quickly scored another one.
Berardi forced a save from Rui Patricio at the near post, having nutmegged Leonardo Spinazzola, the goalie pulled it back for Laurienté to drill home from 10 yards.
Roma later halved the deficit with a lucky goal. Spinazzola floated a cross to the back post for Nicola Zalewski, whose volley into the ground bounced over a surprised Consigli. It looked unintentional, as it was with his weaker foot that counted as his first senior goal for the club.
In the search for an equaliser, Wijnaldum nodded Zalewski’s cross wide while Laurienté blasted over from inside the box.
Rui Patricio was called into action again when he flew to palm a Pinamonti effort out from under the bar.
Things went from bad to worse for the hosts as they were reduced to ten men in first-half stoppages. Berardi pounced on a loose ball to force Rui Patricio to save in the six-yard box, but Kumbulla committed a stupid foul by kicking out at the Sassuolo captain in a reaction foul.
After VAR intervention, he was sent off, resulting in a penalty that Berardi converted.
After a top performance during the mid-week, Paulo Dybala and Rick Karsdorp came on to help their team. Roger Ibanez nodded over La Joya’s corner while Berardi’s rocket skimmed the bar.
With an immediate impact, Dybala saw his left foot strike become a perfect finish into the far top corner from the edge of the box for 2-3.
Sassuolo almost restored their two-goal lead 30 seconds later as Berardi unleashed a left-foot strike and cracked a shot against the Roma crossbar.
After a few attempts at goal from Wijnaldum and Zalewski outside the box, Sassuolo added a fourth.
Laurienté threaded through for Pinamonti to delicately dink it over the on-rushing Rui Patricio.
Refusing to give up, Roma, after several efforts at goal, got their third through Wijnaldum.
The Dutchman got his first goal for Roma deep into stoppages, as Smalling’s through ball allowed him to spring the offside trap and chip the ball over Consigli for 3-4.