After a hugely disappointing start to the campaign, Milan boss Paulo Fonseca was already under serious pressure for his job having only arrived in the summer.
He sprung a tactical surprise here, switching to a 4-4-2 formation in an effort to outsmart the Nerazzurri. And, initially at least, it seemed to work as his side opened the scoring inside 10 minutes.
Henrikh Mkhitaryan had his pocket picked by Christian Pulisic, allowing the in-form American to drive at the Inter defence and fire home past a helpless Yann Sommer.
Simone Inzaghi’s men needed time to settle, but a Lautaro Martínez half-volley that flashed over seemed to inject some life into their performance.
And the reigning champions built on that foundation to restore parity before the half-hour through Federico Dimarco, with the wing-back arrowing into the bottom corner after being slotted through Martínez.
Inter were in the ascendancy from there, and only a tremendous fingertip save from Mike Maignan prevented the ‘hosts’ from going into the break ahead.
Half time came at a good time for Fonseca, as his side were hanging on towards the end of the first period. Rested and recovered, Milan flew out of the traps and threatened to restore the lead within a minute of the restart.
Emerson Royal brilliantly scooped a cross from the byline to find the arriving Rafael Leão, but his bullet header was tipped over by Sommer. The Swiss had to be on guard again to deny Tijjani Reijnders, whose snapshot took a wicked deflection towards the bottom corner before the Inter stopper intervened.
With 20 minutes remaining, the contest opened up, and Martínez let fly with a first-time volley that stung the palms of Maignan.
At the other end, Sommer made a smart stop to deny Leão after an electric Rossoneri counter, before Tammy Abraham lashed wide from a promising position on the inside right.
With energy levels dropping, it looked as though this thriller was heading for a stalemate. Gabbia had other ideas though, rising highest to power a bullet header into the corner from Reijnders’ delivery to breathe fresh life into the Rossoneri’s season.
Flashscore Man of the Match: Tijjani Reijnders (AC Milan)
