Chelsea’s second assistant coach Marco Ianni provoked Mourinho after Ross Barkley’s late leveller in the sixth minute of stoppage time in the 2-2 draw.
Immediately after Barkley scored, Ianni got up and did a first pump in front of the United dugout, which Mourinho ignored.
However, Ianni continued to celebrate in a demonstrative manner and ran past the United dugout.
On this occasion Mourinho was livid and reacted angrily, attempting to chase Ianni down the tunnel before being held back, with members of the coaching staff from both teams involved.
Chelsea manager Maurizio Sarri also celebrated with a fist-pump, but it was Ianni who incurred Mourinho’s wrath with his actions.
The incident sparked a mass brawl between the players and Chelsea fans responded by chanting ‘f*** off Mourinho’ at their former manager.
Mourinho issued a riposte after the final whistle by making a three-finger salute to the Chelsea fans after the game in reference to three Premier League titles that he won while with the Blues.
Chelsea opened the scoring through Antonio Rudiger in the first half before Anthony Martial’s second-half brace saw United take control of the game only for Barkley to equalise.
The result means that United have won just one of their last six matches in all competitions.