The Rossoneri find themselves 18 points adrift of leaders Napoli after suffering a fourth consecutive defeat in all competitions.
Stefano Pioli’s Milan came into the contest under intense scrutiny, after overseeing consecutive defeats while conceding 4+ goals.
Going into the weekend, only three sides in the division had conceded more first-half goals than Milan, so an Inter opener seemed inevitable.
That goal would eventually arrive through the irrepressible Martínez, who netted for the seventh time against the Rossoneri with a trademark near-post header that left Tătărușanu helpless.
The goalkeeper’s frustration after conceding was clear and no doubt shared by everyone of a Milan persuasion, as his side had failed to register a single shot by the time HT arrived.
The battle of wits between Tătărușanu and Martínez continued after the interval, with the Milan goalkeeper again on hand to prevent Inter from extending their advantage.
Perhaps complacency had set in amongst Simone Inzaghi’s players after the first half was so comfortable, but his team struggled to match Milan’s intensity after the break and found themselves doing the lion’s share of the defending.
With confidence low though, Milan failed to adequately test Andre Onana, who remained little more than a spectator as the Rossoneri fell to a fifth straight league game without a win.
Inter, meanwhile, remain Napoli’s nearest challengers at the top of the table, but still sit a huge 13 points adrift after 21 games.