The Belgian slid in to convert a fine through-ball from former Viola attacker Adem Ljajic as Rudi Garcia's men made light of the absence of suspended striker Mattia Destro
The Belgian struck midway through the second half, slotting home a sublime through-ball from former Viola ace Adem Ljajic, as the Giallorossi once again drew to within eight points of the Bianconeri, who had defeated Bologna 1-0 earlier in the evening.
Both sides went into the game without a host of first-team regulars through injury but it was the absence of the suspended Mattia Destro that proved most decisive, as it resulted in a start for Ljajic against his old club.
The Serbian did not pass up the opportunity to show the Viola what a talent they let go last summer.
Indeed, Ljajic created what should have been the opener just nine minutes in when he broke away down the left flank before rolling the ball across the area for an unmarked Gervinho. However, the Ivorian, with the goal at his mercy and just Neto to beat, criminally side-footed the ball wide of the far post.
Ljajic was not to be denied his seventh assist of the season, though. In the 26th minute, he weaved his way across the Fiorentina box, skipping past a couple of challenges, before slipping a pass through for Nainggolan, who went to ground to help the ball past Neto and into the back of the net.
Vincenzo Montella's men responded well to that setback, though, and Jospip Ilicic's set-piece prowess twice very nearly dragged his side back into an absorbing encounter.
First, the Slovenian saw a free kick flash just over the bar, and then, another set-piece special appeared to strike the arm of Roma skipper Francesco Totti.
The Viola's furious appeals were waved away by referee Paolo Silvio Mazzoleni and the Giallorossi went in a goal to the good at the interval.
The excellent Ljajic could have made it 2-0 just moments after the restart but Neto was equal to his curling effort.
The Fiorentina shot-stopper also dealt well with a well-struck Totti drive midway through the second half to keep his side in contention.
In truth, though, the hosts never really looked like equalising, with a 72nd-minute header from Stefan Savic that sailed just wide the best they could muster.
Indeed, they were once again reduced to desperate appeals for a penalty right at the death, when Alessandro Matri's goal-bound shot struck Rafael Toloi on the hand, but the Brazilian's arms were firmly by his side and Roma justly departed the Artemio Franchi with all three points - and their fading title dream still alive.