Title holders Inter failed to secure their third successive league after being held to a goalless draw by Genoa.
A sole point would have been enough for the defending champions to stay one point ahead of their chasers, but their 10-men opponents clinched a hard-fought draw.
The match was ill-tempered and witnessed a multitude of cautions for both sides in addition to a red card handed for Genoa's Domenico Criscito.
Udinese moved top after compounding Roma's misery with a 3-1 victory.
Pasquale Marino's men, who now have 17 points, enjoy a superior goal difference over Napoli and Inter.
Roma, who suffered a crushing 4-1 defeat to Inter last week, have been stumbling for quite a while, which paved the way for the home side to narrowly secure the top spot.
An Antonio Flores strike midway through the first half in addition to a brace from Antonio Di Natale either side of the interval condemned Roma to another defeat.
The Giallorossi scored a consolation through skipper Francesco Totti on 74 minutes.
Meanwhile, early pacesetters Lazio slumped to their second consecutive defeat after losing to Napoli 1-0, thanks to Sebastiano Siviglia's own goal.
Napoli trail Udinese and Inter Milan by few goals.
Elsewhere, Brazilian scoring sensation Kaka led AC Milan to an away 1-0 victory over Atalanta, to keep the Rossoneri right behind the joint leaders with 16 points.