A double from Fiorentina's in-form Dusan Vlahovic ensured Lazio missed the chance to close the gap on the Serie A top four as they slipped to a 2-0 defeat away on Saturday.
The Serbian striker, who has been linked with a move to a host of top clubs around Europe, edged Fiorentina in front with his 20th league goal of the season in the 36th minute.
The hosts were good value for their lead as other than a superb Bartlomiej Dragowski save to deny Joaquin Correa, the visitors did not muster another shot on target in the opening period.
As Lazio pressed for a leveller, Vlahovic headed home his ninth league goal in his last seven appearances late on to inflict a damaging defeat on the side from Rome, leaving them on 65 points, four behind Juventus, who play on Sunday, in fourth.
To compound a miserable evening for Lazio, Andreas Pereira was sent off in stoppage time for two bookable offences.
A much-needed victory for Fiorentina saw them climb to 13th, seven points clear of the relegation zone.