AC Milan produced one of their best performances in recent years to complete a horrible few days for Inter Milan.
Alex had given AC Milan the lead ten minutes before half-time. Only for the same player to give away a penalty on 70 minutes.
Argentine striker Mauro Icardi hit the post with his spot kick and AC Milan made Inter pay in stunning style.
Carlos Bacca made it 2-0 three minutes later and Mbaye Niang, who had crossed in for the second, added a third on 77 minutes.