Champions Inter, who lost at Juventus on Sunday, moved back up to third spot and are five points behind leaders Milan having now played the same number of games.
Inter went ahead after six minutes when Maicon's cross was diverted into his own net by Michele Camporese but mid-table Fiorentina levelled on 33 minutes when Manuel Pasqual's ball into the box crept in at the far post without being touched.
Coach Leonardo handed a first start to Japanese left-back Yuto Nagatomo and had Dejan Stankovic fit again after injury but Inter still laboured until Pazzini turned in Samuel Eto'o's low cross 17 minutes into the second half.
Playmaker Wesley Sneijder was substituted with an apparent groin problem late on to put a slight dampener on the win with Inter only having 13 matches left to overhaul Milan and second-placed Napoli in pursuit of their sixth straight title.
The Inter game was rearranged because of their involvement in December's Club World Cup, which they won as European champions but led to boss Rafa Benitez being replaced by Leonardo following a rant about a lack of signings.
Genoa also beat city rivals and fellow mid-table side Sampdoria 1-0 on Wednesday in a game which had been postponed because of snow in December. Brazilian Rafinha grabbed the goal 10 minutes into the second half in one of Serie A's most colourful and heated derbies.
