Marco Parolo scored twice as Lazio heaped more woe on Milan, who had Philippe Mexes sent off in a 3-1 defeat.
Lazio came from behind to pick up a deserved three points against a faltering AC Milan side, winning 3-1 on Saturday.
West Ham’s Ravel Morrison has agreed to join Italian side Lazio on a free transfer at the end of the season.
Juventus moved five points clear in Serie A with a 4-0 win over Hellas Verona on Sunday, while Sampdoria beat Parma.
Gonzalo Higuain's first-half goal gave Napoli a 1-0 victory over Lazio at the Stadio Olimpico on Sunday.
Cagliari coach Gianfranco Zola was unable to beat his old club Parma in the Coppa Italia as the hosts edged through 2-1.
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