Emmanuel Gyasi's last-gasp winner handed Spezia a 2-1 victory at AC Milan, as the hosts missed the chance to go top of Serie A.
Rafael Leao had given AC Milan the lead in first-half stoppage time but Spezia came back in the second half.
Kevin Agudelo levelled things up before Gyasi struck the winner in the sixth minute of stoppage time to leave AC Milan in second, two points behind their local rivals Inter. Spezia jumped up to 14th.
Cristiano Biraghi struck twice as Fiorentina stormed to a 6-0 thrashing of Genoa.
Alvaro Odriozola opened the scoring in the 15th minute, with Giacomo Bonaventura doubling the home side's tally in the 34th minute.
Biraghi then struck either side of half-time, with Dusan Vlahovic and Lucas Torreira also adding their names to the scoresheet.
Napoli closed the gap to Inter to just four points after a 2-0 win at Bologna.
Hirving Lozano struck twice to give his side victory.