Inter missed the chance for a fourth straight Serie A victory as Luca Caldirola's late equaliser snatched a 2-2 draw for Monza on Saturday.
Simone Inzaghi's men ended leaders Napoli's unbeaten start to the season on Wednesday, and they got off to a great start at U-Power Stadium as Matteo Darmian fired in from Alessandro Bastoni's cross.
Ater Patrick Ciurria superbly levelled, Lautaro Martinez looked to have earned Inter victory when he took advantage of Pablo Mari's error to smash his side 2-1 ahead.
However, substitute Caldirola nodded home in the 93rd minute to spark jubilant celebrations from the hosts and deny Inter all three points.
Inter were ahead after 10 minutes, Darmian sneaking in at the back post to sidefoot past Michele Di Gregorio from Bastoni's pinpoint delivery.
But their lead would last just a minute, as Ciurria levelled with an exquisite curling finish that gave Andre Onana no chance.
Inter restored their advantage after an almighty mix-up in the Monza defence, with Martinez dispossessing Mari in the hosts' penalty area before smashing home his eighth league goal of the campaign.
Martinez could have added his second shortly after half-time, but his header from Federico Dimarco's free-kick flew just over.
With Monza ramping up their search for another equaliser, Onana was equal to substitute Filippo Ranocchia's long-range free kick, though Martinez hit the post at the other end with a right-footed strike.
Heading into injury time, it looked like Inzaghi's side would be moving just five points behind Napoli ahead of the Partenopei's visit to Sampdoria on Sunday, but Caldirola popped up in the box to nod Ciurria's delivery past Onana and prevent Inter picking up three crucial points in the title fight.
What does it mean? Inter suffer late heartbreak
It was not perfect from Inter as they conceded for a 13th straight Serie A away match, but it appeared they had done just enough to add another three points to their tally in their chase of leaders Napoli.
But they were made to pay for not killing the game off, having registered 1.66 xG (expected goals) to Monza's 1.41, as Caldirola rose highest to loop in a headed equaliser. It could have been worse for Inter, as Onana made a crucial third save of the match to deny Caldirola a winner with a 95th-minute chance.
Martinez the hero
Inzaghi is blessed with four great forwards, but with Martinez preferred to Romelu Lukaku and Joaquin Correa to play alongside Edin Dzeko, he justified his selection with an impressive display.
Aside from scoring what he thought was the winner, Martinez was a terror for Monza's defenders all game long, leading his team in touches in the opposition box (nine) and shots (four), though he perhaps should have scored a second with his 0.56 xG, hitting the post and nodding a good chance over.
Mari a relieved man
Monza responded superbly to going 1-0 down, and looked as if they may have a chance of kicking on to a shock victory after Ciurria's excellent strike to level.
But after Mari carelessly lost possession in his own box for Martinez to put Inter back in front, he will be incredibly thankful Caldirola was able to snatch a late point for Monza.
His first-half howler was the lowlight of a poor display in which he failed to win a tackle or make an interception and committed two fouls. It was a nervy display, and the former Arsenal man is perhaps lucky Inter did not take more advantage.
Key Opta Facts
Martinez has been involved in 11 goals in Serie A in 2022-23 (8 goals + 3 assists), a joint-record alongside Rafael Leao, Victor Osimhen and Khvicha Kvaratskhelia.
In addition, he has been involved in seven goals in his last seven games started in Serie A (5 goals + 2 assists).
Caldirola returned to score in Serie A after 833 days, following his brace on 26 September 2020 for Benevento against Sampdoria.
Inter have conceded goals in their last 13 Serie A away games (7W, 1D, 5L); the Nerazzurri have not recorded a longer run of away matches conceding at least one goal since the period between May 1987 and October 1988 (18 games with goals conceded in that case with Giovanni Trapattoni as coach).
Only Napoli and Inter (both 13) have scored with more players than Monza (12) in Serie A this season.
Inter are in Coppa Italia action on Tuesday, when they host second-tier Parma in the round of 16. Monza meanwhile will travel to face struggling Cremonese in Serie A on Saturday.