Zlatan IbrahimoviÄ's comeback appearance added much-needed urgency but little else for AC Milan as they were held by Sampdoria to 0-0 in Serie A on Monday.
The 38-year-old IbrahimoviÄ, who helped Milan to their last Serie A title in 2011, has rejoined the club until the end of the season with an option for another year.
"Ibrahimovic's impact was absolutely positive," Milan coach Stefano Pioli said. "He immediately gave support. The team is still not used to this presence. At the end we could have looked for him more, his physical prowess gives us an extra solution."
AC Milan's Zlatan Ibahimovic applauds fans during the Serie A football match between AC Milan and Sampdoria at the San Siro stadium. AP
Around 60,000 fans flocked to San Siro for the return of IbrahimoviÄ after nearly eight years, and there was a banner dedicated to him which read: "A new challenge to live together: welcome back Ibra."
However, another banner also recalled the embarrassment of AC Milan's last match, their worst result in 21 years, as it simply read: "Atalanta-Milan 5-0."
Milan failed to score for the third successive match.
IbrahimoviÄ was sent on in the 55th minute for Krzysztof PiÄ tek after Sampdoria started the second half very much on top.
The introduction of the Swede appeared to give Milan impetus, and IbrahimoviÄ had a couple of chances early on but neither of his headers troubled Sampdoria goalkeeper Emil Audero.
IbrahimoviÄ also set up a great chance for Suso in the 77th but the Spaniard fired wide of the left post prompting resounding jeers from the Milan fans.
Ronaldo on fire
Cristiano Ronaldo scored a hat trick and set up the other goal for Gonzalo Higuain as Juventus eased past Cagliari 4-0.
Juventus remained level on points at the top of the league with Inter Milan, which won at Napoli 3-1.
Ronaldo ended 2019 on a scoring streak and he started where he left off, becoming the first player to score at least one goal in one of Europe's top five leagues in each of the last 18 years (2003-20). Real Betis midfielder JoaquÃn and Werder Bremen's Claudio Pizarro are the only active players who can achieve this.
There was little sign of what was to come in the first half but Ronaldo broke the deadlock four minutes after the break, rounding the goalkeeper and depositing into an empty net.
The Portugal international doubled Juve's lead in the 67th and set up Higuain nine minutes from time before completing his hat trick a minute later.
Ronaldo took his tally to eight goals in his past five league matches and 13 for the season.
Romelu Lukaku scored twice and Lautaro Martinez also was on target in Inter's first win at Napoli's San Paolo Stadium since 1997.
Lukaku scored early with a solo effort, taking the ball in his own half and finishing it off by curling a shot around a defender in off the post.
Poor goalkeeping helped Lukaku to his second a half-hour in with a shot through Alex Meret's legs.
Arkadiusz Milik pulled one back for Napoli before the break from close range but Martinez restored the two-goal advantage after the hour mark from close range after a failed interception from Kostas Manolas.
It was Napoli's second loss in three matches since Gennaro Gattuso replaced Carlo Ancelotti as coach.
Atalanta emulated their last result before the winter break with a 5-0 win over Parma.
Alejandro "Papu" Gomez, Remo Freuler and Robin Gosens scored by halftime. Josip Ilicic added two after the restart.
Atalanta moved to within one point of fourth-placed Roma and the final Champions League spot.
Elsewhere, Giuseppe Iachini's debut as Fiorentina coach was ruined by a stoppage-time equalizer from Bologna in a 1-1 draw; and Rodrigo De Paul scored a late goal for Udinese to beat Lecce 1-0.
The games were played on Monday because of the Epiphany, a public holiday in Italy.