Gonzalo Higuain cancelled out Marcos Alonso's opener as Napoli drew 1-1 at Fiorentina, while Sassuolo beat fellow European hopeful Lazio.
Napoli and Fiorentina lost ground on champion Juventus in the Serie A title race as they played out a pulsating 1-1 draw at the Stadio Artemio Franchi.
Both goals arrived early, with each side seemingly keen to atone for last week's Europa League exits – Fiorentina losing out to Tottenham, while Napoli came off second best against Villarreal.
The host struck first in the sixth minute when Marcos Alonso glanced in a header from Borja Valero's corner, but the goal-scorer was culpable when Napoli leveled from the restart.