AC Milan needed to win to avoid losing further ground on their rivals, with Inter Milan, in fourth, after a 2-0 win over Cagliari
Spanish midfielder Suso scored a brace to end his Serie A goal drought as AC Milan got back winning after three consecutive draws with a 4-1 success which thwarted Sassuolo's bid to go second in Serie A on Sunday.
Champions Juventus had maintained their perfect start to the season on Saturday with a 3-1 win in their top-of-the-table clash with Napoli who remain in second place.
Juventus, with a maximum 21 points after seven games, are six points ahead of Carlo Ancelotti's team as they target an eighth consecutive Scudetto.
AC Milan needed to win to avoid losing further ground on their rivals, with Inter Milan, in fourth, after a 2-0 win over Cagliari, and Roma, in eighth, after a 3-1 derby win which halted the four-match winning streak of city rivals Lazio.
"This result can help us gain confidence," said Milan coach Gennaro Gattuso.
"When you wear the Milan jersey and work at a glorious club like this, which wants to get back to the top, there is pressure.
"People aren't so much interested in performances as results and the table, but I knew this team had promise and just needed some time to grow."
Despite the win Milan remain tenth in the standings, four points off Inter Milan, who occupy the final Champions League berth.
Unheralded Sassuolo -- a surprise high flyer early this season -- dropped to fifth, equal on 13 points but behind Fiorentina and Inter Milan on goal difference.
"We have a lot of young and talented players, so we don't know how far we can go, but there will inevitably be setbacks like this as part of the growth process," said Sassuolo coach Roberto De Zerbi.
AC Milan's victory came despite the absence of star striker Gonzalo Higuain with forwards Patrick Cutrone and Fabio Borini also out injured.
Suso scored his first league goal since February five minutes after the break in Modena after Ivorian Franck Kessie had put Milan ahead with a brilliant solo run on 39 minutes.
Samu Castillejo added a third on the hour mark before Filip Djuricic pulled one back for the hosts.
Suso got his second goal four minutes into stoppage time after consultation with the video assistant referee (VAR).
Sassuolo's defeat allowed Fiorentina to move third with a 2-0 win over Atalanta.
Bergamo-based Atalanta travelled to Fiorentina's Artemio Franchi stadium desperate to end a five-game winless streak.
But their hopes were jolted just after the hour when referee Paolo Valeri pointed immediately to the penalty spot, refusing to consult VAR despite Federico Chiesa going down easily from Rafael Toloi's challenge.
Jordan Veretout stepped up to slot the ball past Pierluigi Gollini after 63 minutes, and Fiorentina cemented the win when Cristiano Biraghi doubled their lead in stoppage time.
At the final whistle, tensions boiled over with furious Atalanta coach Gian Piero Gasperini confronting Fiorentina counterpart Stefano Pioli before the pair were dragged apart.
"He shouted at me that the penalty was non-existent," said Pioli.
Gervinho has now scored as many goals in Serie A this season (3) as Cristiano Ronaldo.— Squawka Football (@Squawka) September 30, 2018
More than one high-profile name turning out in black and white this season. 😉 pic.twitter.com/pJUshEOgZQ
"They gave a penalty against us for a fingertip against Inter, so this time they gave one in our favour for light contact," added Pioli, whose side lost to Inter Milan midweek.
"We were tenacious, a little lucky."
Elsewhere, Polish striker Krzysztof Piatek became the first Serie A debutant in 68 years to score eight goals in the opening six games when he hit a brace for Genoa, who have a game in hand, in a 2-1 win over Frosinone.
Piatek got his first after 33 minutes, adding a second three minutes later.
Camillo Ciano gave promoted Frosinone their first goal of the season when he converted a penalty four minutes before the break.
Torino got back to winning ways with substitute Simone Zaza sealing a late winner against tailenders Chievo.
Federico Santander scored one and set up substitute Riccardo Orsolini as Bologna came from behind to beat Udinese 2-1.
Ivory Coast forward Gervinho got his third goal in five games as midtable Parma edged Empoli 1-0, in a showdown between two promoted teams.
Bologna 2 (Santander 42, Orsolini 82) Udinese 1 (Pussetto 32)
Chievo 0 Torino 1 (Zaza 88)
Fiorentina 2 (Veretout 63-pen, Biraghi 90+4) Atalanta 0
Frosinone 1 (Ciano 41-pen) Genoa 2 (Piatek 33, 36)
Parma 1 (Gervinho 33) Empoli 0
Sassuolo 1 (Djuricic 68) AC Milan 4 (Kessie 39, Suso 50, 90+4, Castillejo Azuaga 60)