Inter moved up to within five points of city rivals and Serie A leaders AC Milan after they won 2-1 at Fiorentina on Wednesday.
The defending champions climbed above Lazio and into third place with the victory, Inter's eighth in 10 league matches since Leonardo took over from Rafael Benitez in late December of last year.
Marco Camporese own goal gave Inter the perfect start with just six minutes on the clock.
But Sinisa Mihajlovic's side responded well and hit back with a goal of their own just after the half-hour mark when defender Manuel Pasqual found the back of the net.
As the game opened up and both sides searched for a winner, Inter snatched a vital goal on 62 minutes when Giampaolo Pazzini struck for the fourth time in five matches for his new club.
Italy international Pazzini has already made a big impact at Inter since joining in the January transfer window from Sampdoria, with his goal giving Leonardo the response he would have craved after his side were 1-0 losers at Juventus on Sunday.
In Wednesday's other match, Genoa claimed a 1-0 win at Sampdoria in a tense local derby that sent Davide Ballardini's side ahead of their rivals on the table.
Brazilian defender Rafinha scored the game's only goal after 55 minutes and, despite a raft of attacking substitutions, Sampdoria could not find the all-important equalizer.
After losing Pazzini to Inter and Antonio Cassano to AC Milan in January, Sampdoria have struggled to find a replacement, with Palermo signing Massimo Maccarone and Manchester United loanee Federico Macheda battling to fill the void of the departed duo.
