Cristiano Ronaldo scored a second-half hat-trick to lead Serie A champions Juventus to a 4-0 win at home to Cagliari on Monday, taking his tally to eight goals in his last five league games.

The Portuguese pounced on a mistake in the Cagliari defence to break the deadlock four minutes after half-time, before adding the second from the penalty spot as he scored for the fifth league game in a row.

After setting up Gonzalo Higuaín for the third in the 81st minute, he completed the rout by finishing off a counterattack one minute later.

The win left Juventus top of Serie A with 45 points from 18 games, at least until Internazionale, who are three points behind, visit Napoli in the evening match. Ronaldo took his tally this season to 15 goals, including 13 in Serie A.

Leaders Internazionale beat Napoli 3-1 at the San Paolo. Romelu Lukaku scored twice for Inter before Arkadiusz Milik pulled one back for the hosts. Any hope Napoli had of a comeback were extinguished when Lautaro Martínez scored Inter’s third on 62 minutes.

Romelu Lukaku scored twice in Naples. Photograph: Tiziana Fabi/AFP via Getty Images

Zlatan Ibrahimovic’s return failed to inspire Milan as the fallen giants were held to a 0-0 draw at home by Sampdoria, failing to score for the third league game in a row.

The charismatic 38-year-old Swede was brought on to a rousing reception from the San Siro crowd in the 55th minute but Milan could still not find a way past their lowly opponents. In his previous stint at the club, Ibrahimovic helped Milan win Serie A in 2010-11, their last major trophy. He left for Paris St Germain at the end of the following season. Milan also drew their previous home game 0-0, against Sassuolo, and this result left them a miserable 12th in the Serie A standings, below Verona on goal difference.

In between, Milan were thrashed 5-0 by Atalanta, who beat Parma by the same scoreline with Josip Ilicic scoring twice to close in on the top four, while Riccardo Orsolini’s injury-time free-kick salvaged a 1-1 draw for Bologna at home to Fiorentina.