JOIN USMirko Vucinic's and Marco Cassetti's first-half goals put Roma on 68 points, one more than Inter, who drew 2-2 at Fiorentina on Saturday as their domestic form falters under the stress of reaching the Champions League semifinals.
Third-placed AC Milan's title hopes diminished after they slipped four points off the pace with five games to go despite coming from 2-0 down to draw 2-2 at home with Catania thanks to Marco Borriello's double.
The title race is far from settled but the leadership change still marks a remarkable reversal.
Inter had been in sole command since October and looked to be cruising to a fifth straight scudetto in mid-February when they led by nine points. By contrast, Roma have rallied after they were in seeming disarray early in the season when Claudio Ranieri replaced Luciano Spalletti.
Montenegro forward Vucinic put them ahead on 12 minutes with the help of a blunder by Atalanta keeper Andrea Consigli, who allowed a powerful but direct shot to slip through his grip. Cassetti headed in a Francesco Totti cross in the 27th minute as Roma extended their unbeaten league run to 23 matches. Simone Tiribocchi capitalised on some poor defending to pull one back.