Inter Milan's crisis intensified on Sunday with a 2-1 defeat at Chievo, where Samuel Eto'o appeared to commit a Zinedine Zidane-like headbutt that could result in a lengthy suspension.
Inter president Massimo Moratti gave coach Rafael Benitez his backing after last weekend's derby defeat by leaders AC Milan, but another loss has left the Spaniard exposed with the champions now nine points off top spot.
Eto'o was not cautioned by the referee for his headbutt, but the Cameroon striker could be punished retrospectively.
He scored Inter's consolation goal late on after Sergio Pellissier and Davide Moscardelli put Chievo two up.
Second-placed Lazio also lost ground on Milan after a 1-1 draw at Parma that left the gap at three points. Milan had beaten Fiorentina 1-0 on Saturday.
Juventus won 2-0 at Genoa on Sunday to go third, fourth-placed AS Roma beat Udinese 2-0 on Saturday.
With fives sides above Inter after 13 games, last season's treble winners have a fight on their hands to win a sixth successive scudetto given their poor form and injuries.
Pellissier's first-half header and Moscardelli's second-half strike secured Chievo's victory, but the game will be remembered more for the league's top scorer, Eto'o.
In a moment of madness similar to France midfielder Zidane's assault on Italian Marco Materazzi in the 2006 World Cup final, Eto'o headbutted Cesar in the chest after being hit by the defender earlier.
The officials missed the first-half incident but Serie A is sure to look at video evidence and will almost certainly hand the Cameroonian a lengthy ban, depriving Inter of their leading striker.
Eto'o netted his ninth goal of the Serie A season in stoppage time on a rain-sodden Verona pitch, where Italy's rugby side had played last weekend.
Inter had three youth team players on the bench because of their injury problems, which Benitez has said are bad luck and nothing to do with his changing the team's training regime after taking over from ex-coach Jose Mourinho.
Juventus have had a raft of injuries, too, but winger Milos Krasic returned from his knock to score in the win over Genoa.
The visitors had taken a fortunate lead when Claudio Marchisio's deflected shot cannoned in off the post and the back of Portugal keeper Eduardo.
In the pick of the other Sunday matches, Giampaolo Pazzini scored a hat-trick in Sampdoria's thrilling 3-2 win at Lecce, where Sampdoria striker Antonio Cassano was again omitted following his row last month with the club president.
New Cagliari coach Roberto Donadoni got off to a winning start with a 2-1 comeback victory at Brescia.