Inter Milan's seven-game winning streak was snapped as they were beaten 1-0 at relegation-threatened Lecce on Sunday.
Inter's cross-city rivals AC Milan kept up their pursuit of Juventus at the top of Serie A with a comfortable win over Cagliari at home.
Zlatan Ibrahimovic and Antonio Nocerino found net in the first half with Massimo Ambrosini scoring the third of a one-sided game in the second half.
"It was important for us to win tonight," said Milan head coach Massimiliano Allegri. "We're still close to Juve and have broken away from the chasing pack, as both Udinese and Inter lost this weekend."
Inter had won their last seven Serie A games as they launched an unlikely title challenge under Claudio Ranieri following their miserable start to the season.
But Guillermo Giacomazzi scored for Lecce five minutes before half-time and Inter, despite having two goals disallowed, could not find a response, leaving them nine points behind leaders Juventus, who beat Udinese on Saturday.
Inter head caoch Claudio Ranieri praised Lecce's outstanding defence.
"Today we came up against a great goalkeeper and a team that defended very well," he said.
"We then got too anxious and weren't sharp enough in attack. We also hit the woodwork and had two goals quite rightly disallowed, so were unable to get through a difficult game," he said.
Lazio remain on the fringes of the title race after an impressive 3-0 win at Chievo.
Roma's four-match winning run came to an end as Bologna held them to a 1-1 draw at the Stadio Olimpico.
Genoa held on for a dramatic 3-2 win over Napoli, almost throwing away a three-goal lead as they returned to winning ways after their crushing defeat at Palermo last weekend.
Fabrizio Miccoli starred and Igor Budan headed both goals as Palermo saw off basement club Novara 2-0.
Fiorentina claimed their first win at home since December 4 with a 2-1 triumph over struggling Siena. A Marco Rossi own goal handed 10-man Atalanta a narrow 1-0 triumph at Cesena.