Cagliari piled the pressure on under-fire Roma manager Zdenek Zeman after leaving the capital with a shock 4-2 victory yesterday.
Roma are now winless in six games since returning from the winter break, and the defeat leaves them in eighth place on 34 points, three points behind Milan in fifth place and nine away from the third Champions League spot.
Cagliari climb up to 14th on 24 points after their impressive counter-attacking display.
Radja Nainggolan's smart third-minute goal put Cagliari ahead but a thumping free-kick 10 minutes before half-time by Roma captain Francesco Totti levelled it up.
Roma keeper Mauro Goicoe-chea gifted Cagliari the lead a minute into the second half when, under no pressure, he dropped Danilo Avelar’s cross into the net.
Eight minutes later Marco Sau extended Cagliari’s lead and Francesco Pisano compounded Zeman's misery when after Sau's curling shot cracked against the bar he calmly tucked home his first goal of the season.
Marquinho scored an injury time goal that will be of no consolation for Zeman.