Veteran forward Luca Toni scored twice to hand modest Verona a 2-0 win over Napoli which increased the pressure on coach Rafael Benitez in Serie A.
Bottom-of-the-table Parma's troubles continued as they lost 4-1 at Sassuolo, playing the last half hour with 10 men, while Chievo eased their relegation worries with a 2-0 win at Genoa.
Napoli are now in danger of losing third spot, which earns a place in the Champions League qualifying rounds, after taking only one point from their last nine.
They remained joint third with 46 points alongside Lazio, but their rivals have a game in hand and visit Torino tomorrow.
Toni, 37, opened the scoring when he forced his way through the Napoli defence to score from a narrow angle after seven minutes.
He struck again early in the second half, turning the ball in from close range from Emil Hallfredsson's counterattack after a Napoli move broke down.
There were 12 yellow cards in an often unsavoury match in which Verona's Jacopo Sala was sent off for a second booking in the 89th minute.
Benitez is likely to be under fire for his controversial rotation policy after leaving Gonzalo Higuain, Manolo Gabbiadini and Jose Callejon on the bench at the start.
Parma, who face a bankruptcy hearing on Thursday, were left 11 points adrift at the bottom after another miserable afternoon at Sassuolo, who had lost their last four games.
Nicola Sansone scored twice while Andi Lila replied in between as Sassuolo led 2-1 at halftime.
The game hinged on a second-half incident where Parma goalkeeper Antonio Mirante was judged to have tripped Sansone and was sent off, while the hosts were awarded a penalty.
Domenico Berardi converted and Simone Missiroli added a fourth in the 65th minute.
Parma have only nine points from their 25 games after having three deducted for breaching financial regulations.
Chievo, in 16th place, moved eight points clear of the relegation zone thanks to Alberto Paloschi's two goals at Genoa. Atalanta, one place below them, are four points clear of trouble after a goalless draw at home to Udinese.