Samuel Chukwueze's 13th-minute strike looked like being the first of a comfortable win but ended up being the winning goal as Milan held on for the points.
David Frattesi poked home the decisive goal in the fifth minute of stoppage time in Udine to maintain Inter's 14-point lead at the top of the table with seven matches left in the season.
Inter Milan have a seven-point lead and a game in hand at the top of Serie A after their closest challengers Juventus fell to a shock 1-0 home defeat to Udinese
Mike Maignan was abused during Udinese' 3-2 defeat to AC Milan on Saturday, which was halted for five minutes in the first half after repeated offensive remarks from behind the goal he was defending
Mike Maignan said that he had first heard monkey chants during Milan's match at Udinese on Saturday when he collected the ball for his first goal kick, after which he "said nothing"
Mike Maignan fired back on Saturday at "ignorant" fans who aimed monkey chants at the France goalkeeper during AC Milan's dramatic 3-2 win at Udinese
Napoli's bid for a first Serie A title since the days of Diego Maradona was further boosted on Saturday after surviving a late scare against Udinese to claim a 3-2 win
Serie A: Paulo Dybala explained the glare by saying he was looking "for a friend who I'd invited to the game".
Serie A: Salernitana cast doubt on Tuesday's game at Udinese when they announced Covid-19 cases had prevented their squad leaving as planned for northeastern Italy.
Serie A: Zlatan Ibrahimovic snatched a late point for AC Milan in Saturday's 1-1 draw at Udinese which gives the Serie A leaders' title rivals a chance to steal top spot, while Juventus drew 1-1 at Venezia to slip up in the Champions League race.
Cristiano Ronaldo was denied a last-gasp winner to save Juventus after they had thrown away a two-goal lead at Udinese, his stoppage time header ruled out for offside in a dramatic 2-2 draw
Serie A: Cristiano Ronaldo scored twice to help Juventus to a 2-1 win over Udinese.
Zlatan Ibrahimovic once again proved that age is just a number as he pulled off an incredible bicycle kick in AC Milan's 2-1 win over over Udinese in Serie A on Sunday.
Juventus need just three more points and the coronation could even come on Saturday, depending on the results of their rivals Atalanta and Inter Milan.
Cristiano Ronaldo scored twice as Juventus bounced back from their first defeat of the season to beat Udinese 3-1 and move top of Serie A on Sunday.
Juventus are two points behind Inter Milan after three games and could be overtaken by city rivals Torino who host promoted Lecce on Monday.
It was Cristiano Ronaldo's fourth goal this season for Juventus.
Despite rape claims against him, Cristiano Ronaldo has travelled with the Italian champions to play Udinese.