Theo Hernandez had a goal harshly disallowed by VAR as Milan were held to a 0-0 draw by Sassuolo in their final home Serie A game of 2019.
In-form Hernandez thought he had scored his third goal in as many games just after the half-hour mark at San Siro on Sunday, only for VAR to rule it out for a handball from Franck Kessie.
Chasing a third successive league win for the first time since last season, Stefano Pioli's side piled on the pressure after the interval, only to be frustrated by some brilliant Gianluca Pegolo goalkeeping.
Substitute Rafael Leao twice beat Pegolo in the closing stages, but the crossbar and then the post came to Sassuolo's rescue.
Early in the game, Giacomo Bonaventura's effort forced Pegolo into an unconvincing save, but Sassuolo's goalkeeper reacted brilliantly to deny Kessie's follow-up.
After turning provider for a Hakan Calhanoglu chance, Hernandez thought he had put Milan ahead with a first-time strike which took a wicked deflection on its way through.
A VAR verdict, however, intervened when picking up what appeared to be Kessie's accidental handball.
A terrible back-pass then left Pegolo in no man's land prior to the break, yet Ismael Bennacer - after rounding the stranded goalkeeper - failed to apply the finish.
Jeremie Boga struck wide as Sassuolo caught Milan on the counter early in the second half, while Gianluigi Donnarumma had to keep out a stinging shot from Georgios Kyriakopoulos.
Bonaventura was denied by a brilliant Jeremy Toljan block, before Pegolo made an outstanding stop from Lucas Paqueta's close-range effort and kept out another Bonaventura attempt.
Veteran goalkeeper Pegolo was beaten late on, but Leao's curling strike cracked away off the bar before the substitute hit the right upright. There was still time for a final stop by Pegolo to deny Hernandez as Milan's efforts proved fruitless.
What does it mean? Milan entrenched in mid-table
It has been a frustrating season for Milan and, approaching the halfway stage, the Rossoneri sit 10th. Pioli will at least be able to take solace in the fact his side are only four points shy of eighth-placed Atalanta, though Milan will require a mighty upturn in form to make a push for the Champions League places.
Hernandez hitting his stride
Though he was unfortunate to have his goal ruled out, Milan's full-back put in another accomplished display in both defence and attack. If there is one bright mark from the Rossoneri's season so far, it is the form of the ex-Real Madrid youngster.
Piatek's struggles continue
Having netted from the spot against Bologna last time out, Piatek will have been hoping for an upturn in his fortunes, but he cut a frustrated figure in a lone striker role and was well contained by Sassuolo's defence.
Atalanta are Milan's final opponents of 2019 on December 22, while Sassuolo face struggling Brescia on Wednesday before rounding off their year against Napoli.