Balde Diao Keita, Sergej Milinkovic-Savic and Felipe Anderson struck as the visitors climbed to ninth with 27 points from 19 matches.
Fiorentina, who replied through Facundo Roncaglia in stoppage time, are third on 38 points, one adrift of leaders Inter Milan who host Sassuolo on Sunday.
Lazio dominated from the start and were rewarded in first-half injury time when Keita, after a fine one-two with Filip Djordjevic, beat Anton Tatarusanu from close range.
Fiorentina looked more lively when Giuseppe Rossi came on for the injured Matias Fernandez in the 74th minute and the substitute immediately curled a shot that was tipped away by keeper Etrit Berisha.
Lazio grabbed a second goal two minutes into added time as Milinkovic-Savic went past two defenders before slotting the ball past Tatarusanu.
Two minutes later Roncaglia pulled one back for the home side when Berisha let slip his routine shot.
Anderson, who had replaced Keita in the 87th minute, wrapped up victory six minutes into injury time when he scored from close range following a sharp counter attack.
Fifth-placed AS Roma failed to ease the pressure on under-fire coach Rudy Garcia as they were held to a 1-1 home draw by AC Milan.
Antonio Ruediger opened the scoring for Roma after four minutes when he latched on to Miralem Pjanic's free kick but Milan equalised five minutes into the second half through Juraj Kucka.
Roma, who are five points ahead of sixth-placed Milan, have won just one of their last nine league games.
Elsewhere, promoted Carpi stayed two points from safety despite defeating Udinese 2-1.
(Writing by Julien Pretot; Editing by Tony Jimenez)
Share
