Following his heroics last week, when he netted a five-minute hat-trick to down Palermo, the Senegalese attacker bagged a brace at the Stadio Olimpico as Lazio claimed bragging rights over their local neighbours.
For his first, Balde received a through ball from deep in midfield and his deflected effort wrong-footed Wojciech Szczesny in the Roma net as he opened the scoring.
Daniele De Rossi converted a controversial penalty to send the sides in locked 1-1 at half-time.
Dusan Basta’s shot at goal deflected off a Roma defender before creeping past Szczesny inside his near post to extend the visitors’ lead before Senad Lulic beat several defenders with a fantastic run from his own half before finding Balde, who slotted home calmly from inside the area to seal a famous derby victory.
The brace took the 22-year-old’s tally to 13 in 28 appearances for Biancocelesti, his best yet in Lazio colours, as he continues to put his troubled start to the campaign behind him. Balde was linked with a move to Real Madrid last summer, and performances like this will continue to see him linked to Europe's top sides.
Egypt's Mohammed Salah also saw the game through but could not save Roma from defeat.