A scorching volley from Theo Hernandez has led to the opening goal, Zlatan Ibrahimovic made his season debut and goalkeeper Mike Maignan returned after five months out during an encouraging 2-0 win for AC Milan over Atalanta in Italy's Serie A.

Sunday's victory moved the defending champions level on points with second-placed Inter Milan, who lost 1-0 at Bologna, 18 points behind runaway leader Napoli.

Hernandez opened the scoring midway through the first half at the San Siro with a long-distance effort that ricocheted off the post then hit goalkeeper Juan Musso in the back before going in for an own-goal.

Milan produced several more chances before Junior Messias finally lifted a shot over the onrushing Musso and into an empty net.

Ibrahimovic came on in the 74th minute and at age 41 and 146 days became the oldest Milan player in recent memory, beating the mark that Alessandro Costacurta had established at 41 years and 25 days.

Ibrahimovic had surgery on his left knee in May, while Maignan injured his left calf in September.

Atalanta failed to have a single shot on goal and remain sixth, six points behind the Milan rivals.

In Bologna, Riccardo Orsolini took advantage of a defensive error by the visitors to score midway through the second half to register consecutive home wins over Inter for the first time since 1999.

Bologna dominated the match and had several other chances, as Inter appeared to lack motivation following their 1-0 win over FC Porto in the Champions League four days earlier.

"We're not going to achieve anything if we play this way," Inter striker Lautaro Martinez said.

"We need to change immediately and find more consistency. We just had a great game in the Champions League and now we put on a performance like this. That's not good."

Elsewhere, Salernitana beat Monza 3-0 and Udinese drew 2-2 with Spezia.