Jose Mourinho and Arsene Wenger have been involved in a touchline fracas during the match between Chelsea and Arsenal at Stamford Bridge.
The two men clashed after Blues defender Gary Cahill was booked for a strong challenge on Alexis Sanchez, with Wenger shoving Mourinho after the Portuguese stepped out of his technical area to complain about the sanction.
An unbalanced Mourinho responded by grasping at his opposite number, and the quarrel continued with a slanging match.
Referee Martin Atkinson was forced to intervene and warned both managers that they would be sent to the stands if there was a repeat of the early flash-point.
Towards halftime, Rui Faria and Steve Bould, assistants at Chelsea and Arsenal respectively, were also involved in an exchange of words as the row continued between both benches.
Mourinho and Wenger have enjoyed a long, sometimes bitter rivalry over the last 10 years.
Last season, Mourinho called his opposite number a "specialist in failure," and in his first spell as Blues boss he claimed the Frenchman was a "voyeur."
An eventful opening period at Stamford Bridge also saw Thibaut Courtois taken off with a head injury following a clash with Alexis, with Petr Cech coming off the bench to replace the Belgian.
Kickoff had already been delayed by 15 minutes after it was claimed security staff needed extra time to remove flares brought to the stadium by Arsenal fans.