The chanting aimed at Sassuolo's Claud Adjapong and Alfred Duncan led to warnings being issued over the loud speakers during Sunday's tie which the Roman side won 6-1.
In its disciplinary report the Lega Serie A found “around 2,000 of the 5,449 occupants” of the section were guilty of “chants expressive of racial discrimination” in the 31st and 77th minutes of the match.
As a suspended sentence had already been applied for the same reason after the Rome derby on April 30 this year the Curva Nord will now be closed for two home games.
In addition to the match against Cagliari on October 22 the Lazio fan section will also be closed against Udinese on November 5th.
Atalanta, meanwhile, have been fined 10,000 euros ($11,748) after bottles were thrown at Juventus players at the weekend.
Juventus sporting director Fabio Paratici was fined 20,000 euros ($23,497) for insulting the Video Assistant Referee (VAR) during the game.
Inter were fined 2,500 euro ($2,937) for delaying the start of their match with Benevento by four minutes, as were Roma with their game against Milan starting three minutes late.