Mauro Zarate's first-half goal was enough to see Lazio return to winning ways and condemn Reggina to relegation after six straight years in Italy's top flight.
Reggina are four points behind 17th-placed Torino with one match remaining.
Lazio had gone into tonight's game at the Stadio Olimpico on the back of four consecutive defeats.
It was Reggina, needing three points in order to keep alive their season-long survival battle, who started the match brightest, Franco Brienza's improvised strike forced Lazio goalkeeper Juan Pablo Carrizo to make a save.
Lazio thought they had taken the lead on 11 minutes when Stephan Lichtsteiner fired past Reggina goalkeeper Christian Puggioni from Goran Pandev's assist only for the goal to be disallowed by the referee for offside.
At the other end, Andrea Costa found time and space on the left-hand side of the box but his dangerous-looking cross eluded everyone in the penalty area and Lorenzo de Silvestri cleared the danger for the hosts.
Reggina almost broke the deadlock midway through the first half but Carlos Carmona's close-range strike was met by a fine save from Carrizo.
Lazio made no mistake on 26 minutes.
Ousmane Dabo's precise through-ball found Zarate's run and the Argentina striker did not even have to break his stride to delicately direct the ball past Puggioni.
The visitors responded well to the body blow of falling behind and just after the half-hour mark, Brienza had a golden opportunity to equalise.
But having dribbled past Carrizo inside the Lazio area, Brienza was unable to find the finishing touch, much to the disappointment of his team-mates.
For all their efforts, Reggina were fortunate not to go into the break with a 2-0 deficit.
A fast counter-attack from Lazio left Pandev with only Puggioni to beat, but the striker's lob went just wide of the far post.
Lazio picked up where they left off and Puggioni was forced to come off his line to anticipate a determined Ettore Mendicino.
Mobido Diakite then made a brave tackle on Bernardo Corradi inside the Lazio area, who was ready to fire past Carrizo.
Shortly after the hour mark, Cristian Ledesma warmed the hands of Puggioni with a powerful free-kick which the goalkeeper cleared.
With time running out and Reggina coach Nevio Orlandi willing his team forward in search of an equaliser, Lazio looked dangerous on the counter-attack.
Aleksandar Kolarov forced Puggioni to fully stretch while seconds later, Mourad Meghni's effort from distance went just over the crossbar.
With eight minutes remaining, Fabio Ceravolo failed to connect with Brienza's cross from the right.
Carrizo then made an heroic save from Brienza's right-footed volley inside the area as the Reggio Calabria outfit tried in vain to find a goal but the match finished 1-0 with Reggina's fate sealed.