Milan drew for the third successive time in Serie A against Parma at the San Siro on Saturday.
The European champions missed the chance to go second and are now three points behind leaders Roma.
Milan took the lead just before half-time when Clarence Seedorf scored on the rebound after Filippo Inzaghi had been denied.
But the hosts were unable to hang on for the win and Andrea Pisanu finished from Reginaldo's cross in the 73rd minute.
Antonio Di Natale continued his excellent recent form with both goals in Udinese's 2-0 home win over Reggina.
Di Natale netted the opener on five minutes when he cleverly chipped Reggina keeper Andrea Campagnolo.
The Italy striker fired home his and Udinese's second just after the hour mark to ensure Reggina remain winless.