Atalanta moved three points clear of AC Milan with their 2-0 victory at the San Siro on Saturday, with former Rossoneri youngster Bryan Cristante scoring a decisive goal for Gian Piero Gasperini’s side.
Josip Iličić also got on the scoresheet for the visitors, punishing AC Milan for their wasteful attacking display.
The game was a slow starter, with Milan largely being kept inside their own half of the pitch.
Nikola Kalinić somehow avoided a red card for an extremely high tackle on Brazilian defender Rafael Tolói, before Giacomo Bonaventura had the ball in the back of the net for the hosts.
However, the Italian midfielder saw his early goal ruled out for a combination of handball, from Patrick Cutrone, and offside.
Leonardo Bonucci, Riccardo Montolivo and Fabio Borini all peppered Etrit Berisha's goal without really being able to test the Albanian goalkeeper, while Atalanta's first opportunity of the game brought about the opening goal of the match.
Alejandro 'Papu' Gómez floated a teasing ball into the back post which was met by Mattia Caldara.
The centre-back's header tested the reflexes of Gianluigi Donnarumma but Bryan Cristante, a former AC Milan academy player, prodded the ball into the back of the net from the rebound to put the visitors in front at half-time.
Ricardo Rodríguez had Milan's first opportunity of the second-half, with Franck Kessié and Nikola Kalinić also firing just wide inside the opening five minutes following the restart.
The hosts were continuing to grow frustrated with their lack of chances, seeing a number of good opportunities go to waste with lady luck firmly staying on Atalanta's side.
The Rossoneri had control of possession and kept Atalanta feeding off scraps, but neither Kalinić, Kessié or Fabio Borini could punish La Dea with their efforts on goal.
Milan were then punished for their wasted chances when Josip Iličić, a second-half substitute, smashed the ball past Donnarumma with a confident finish on his weaker right foot - causing some of the home fans to head for the exits.
Atalanta continued to work hard to keep Milan out, forcing the Rossoneri into hopeful shots from distance and rushed passes in the final third.
The hosts were unable to even find a consolation goal in the final moments of the game, increasing the pressure on the club ahead of the Derby della Madonnina next week.