Luca Pellegrini, Adam Marušić and Matteo Guendouzi all saw red cards in what proved to be a more than busy Friday night for referee Marco di Bello.
Marco di Bello issues a red card to Matteo Guendouzi and hands a yellow to Christian Pulisic. (AP PHOTO)
Another four Lazio players were booked, while five AC Milan players were shown yellow on a bad-tempered evening.
Pellegrini was sent off after 57 minutes when the score was 0-0.
Noah Okafor scored with two minutes remaining and a red mist descended on the Lazio players.
Marušić and Guendouzi were sent off in the dying minutes and players from both sides squared up to each other at the final whistle.
The confrontations followed a mini brawl after Pellegrini's sending off.
Earlier, Lazio coach Maurizio Sarri was booked for arguing with the officials.
Lazio were angered at not being awarded a first-half penalty, while Milan had a goal disallowed for offside with a quarter of an hour remaining.
The result took third-placed Milan to within a point of Juventus. Juventus play Napoli on Sunday.
Lazio remain ninth on the table.
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