Inter Milan lost 2-1 at home to Cagliari Sunday, missing a penalty and suffering as the visitors rallied after a Joao Mario opener.
The Nerazzurri stayed on 11 points and sit in 11th position, 10 points from leaders Juventus. Cagliari are seventh on 13 points after their win.
The Portuguese international Joao Mario struck in the 55th minute, pouncing to flick home after Marco Storari saved his first attempt.
Federico Melchiorri levelled for the Sardinia guests, controlling and tapping in a ball he received after a poor defence clearance in the 71st minute.
A cross from the striker was then turned on by Jaison Murillo and stunned goalkeeper Samir Handanovic, who fumbled into his own goal for the winner with five minutes remaining.
Inter captain Mauro Icardi on 25 minutes had fired a penalty off target after being floored – a mistake that worsened his relationship with fans already bitter over the striker's biography published this week.
He also nodded wide off Cristian Ansaldi three minutes before Melchiorri's equalizer.
"After our goal we had problems, but not before scoring. We did not create many chances, but we did 20 crosses," Inter boss Frank de Boer said. "After scoring we forgot how to play and win the tackles.
"We must understand if it is a mental problem or something else. It must be easier to play when the opponents are pressing because there is more space for us."
Sassuolo fell behind early to their former striker Diego Falcinelli, who then shook the crossbar four minutes after the break.
The bar denied levelling efforts from Gregoire Defrel on three minutes and Lorenzo Pellegrini on 55, but substitutes Stefano Sensi, with a diagonal shot and Pietro Iemmello, from a corner kick, gave the hosts a late win.
Leonardo Capezzi had come close to Crotone's second goal again hitting the bar one minute before Sensi's goal.
Lazio salvaged a 1-1 home draw from a Ciro Immobile's penalty against Bologna, who took a first-half lead from a Filip Helander's flick. The Rome side inched on 14 points and are fourth on goal difference behind Napoli.
Genoa had Darko Lazovic sent off with two bookings 34 minutes into a home game they drew 0-0 with Empoli. Their coach Ivan Juric was also sent off over his protests in the closing minutes.
Earlier in Florence, Fiorentina and Atalanta drew 0-0 in a game that saw the Bergamo guests get no goals from their tactical dominance.
Jasmin Kurtic and Boukary Drame came close in the first half for Atalanta, who sit 13th on 10 points from eight games. The Florence side improved after the break, coming close when Nikola Kalinic missed a header; La Viola are on nine points with a game in hand.
Leaders Juventus moved to 21 points Saturday from a 2-1 home win against Udinese. Roma (16) advanced to second past Napoli (14) by beating them 3-1 in Naples. Pescara and Sampdoria drew 1-1.
Chievo and Milan are both on 13 points when they meet later Sunday. Palermo welcome Torino Monday.