Ronaldo hat-trick in Juve's Serie A win

Cristiano Ronaldo bagged a hat-trick as Juventus beat Cagliari 4-0

Inter Milan have won 3-1 at Napoli thanks to a Romelu Lukaku brace to stay level on points with Serie A leaders Juventus, who earlier on Monday beat visitors Cagliari 4-0 courtesy of a Cristiano Ronaldo hat-trick.

Juve sit top on 45 points from 18 games and lead the Nerazzurri on head-to-head.

Ronaldo, now on 13 league goals, has netted seven times in his past five games.

The Portuguese star has one less than Lukaku, who also struck twice in December before the two-week winter break.

"It was a good start to the year, but the important thing is the team," Ronaldo said.

"We created chances, and scoring is always important. Our game is getting better game by game but we have to work and keep improving."

AC Milan continued their dismal run despite the return of Zlatan Ibrahimovic as they drew 0-0 at home with lowly Sampdoria.

At Turin's Allianz Stadium, Juve played a lacklustre first half but Ronaldo pounced on a bad clearance to strike in the 49th, then netting a penalty on 67 and closing the scoring on 82 off an assist by substitute Douglas Costa.

Gonzalo Higuain, also a second-half substitute, scored the third one minute earlier with a slightly deflected drive.

Lukaku struck off the left post after storming from the midfield and on 33 had a shot fumbled by goalkeeper Alex Meret before the hosts pulled one back from Arkadiusz Milik's flick off a Jose Callejon feed.

Napoli started briskly into the second half, but a blunder from Kostas Manolas allowed Lautaro Martinez to net Inter's third on 62 minutes.

The Neapolitans are eighth on 24 points, two points above 11th-placed Milan.

Ibrahimovic, the 35-year-old Swedish star came off the bench on 55 minutes but could not find a breakthrough at the San Siro.

"We wanted a win and failing to get it was disappointing," Milan coach Stafano Pioli said.

"We played a lot of balls into their midfield but lacked the quality and the precision needed to win the game.

"In my opinion (Ibrahimovic's) impact was positive. He helped the team and was very active.

"Possibly the team are not used yet to his strong personality."

Elsewhere, fifth-placed Atalanta hammered Parma 5-0 with a Josip Ilicic brace while Bologna drew 1-1 with Fiorentina and Udinese won 1-0 at strugglers Lecce.