Lazio, who reclaim fourth spot from Inter Milan and sit four points behind Napoli in third, took the lead at the Stadio Olimpico through Ciro Immobile in the 56th minute.
However, Maxi Lopez headed past Thomas Strakosha from a free-kick to bring Torino level.
But in the closing minutes Torino left huge gaps in their defence on a Lazio counter-attack, and Jordan Lukaku had plenty of time to set up Balde for a strike from outside the area that beat England’s Joe Hart at the goalkeeper’s near post.
Hart had been two metres off his line and despite trying to make amends three minutes later, Felipe Anderson had no trouble firing past the on-loan Manchester City shot-stopper, who appeared to suffer a knock as he came out to block.
Inter had stepped up their bid for a top-three finish with an emphatic 7-1 win over Atalanta at the San Siro on Sunday, but Lazio are now two points ahead of Stefano Pioli’s men in fourth.
Juventus, 2-1 winners over AC Milan on Friday, remain on course for a record sixth consecutive Serie A title and a third consecutive league and Cup double.
Massimiliano Allegri’s men, who take a 2-0 first-leg lead into their last-16 decider at home to Porto in the Champions League on Tuesday, lead Roma by eight points with Napoli 10 points off the pace in third.