Per Kroldrup poked home to earn Fiorentina a point in the 82nd just a minute after Samuel Eto'o looked to have snatched a comeback win for the champions.
Inter's Argentina forward Diego Milito had scored in the 75th minute to cancel out Brazilian Keirrison's opener for the hosts in the 11th.
Second-placed Roma will move a point ahead of Inter, who have 67, with five games to go if they beat relegation-threatened visitors Atalanta when the rest of the league programme is played on Sunday.
AC Milan, who are four points behind Inter in third, face Catania at the San Siro.
Inter looked to be cruising to a fifth straight scudetto in mid-February when they led by nine points but the exertions of reaching the Champions League semi-finals may have contributed to their domestic form stuttering.
"We're not worried and we don't think about what Roma will do," Inter technical director Marco Branca told Sky television.
"They still have to play tomorrow. We played our match today against an excellent team. We could have won. We did what we had to do."
BRIGHT START
Inter coach Jose Mourinho has stopped speaking to media before and after Serie A matches following a series of touchline bans for controversial comments and gestures.
His men made a bright start against a Fiore side who had several regulars initially on the bench, with the teams due to meet again on Tuesday in the Italian Cup semi-final second leg.
Wesley Sneijder and Samuel Eto'o forced good saves out of Fiorentina goal keeper Sebastien Frey and Diego Milito headed a great chance on to the post in the opening exchanges.
Keirrison, starting for Italy striker Alberto Gilardino, soon showed how dangerous the hosts could be though, steering the ball into an empty net to finish a silky move.
Inter coach Jose Mourinho tried to shake things up at halftime by bringing on Mario Balotelli and it looked to have paid off when the teenage forward set up Cameroon striker Eto'o's goal soon after Milito's equaliser.
But Inter, who carry a 1-0 advantage from the first leg into next week's Cup match, made a mess of defending a corner and Denmark's World Cup-bound Kroldrup took advantage.
Earlier, Napoli's hopes of taking Italy's final Champions League qualifying place took a knock when they lost 3-2 at home to Parma and missed the chance to go fourth.
Sixth-placed Napoli stay on 49 points, two behind joint-fourth Palermo and Sampdoria, who are at home to Chievo Verona and city rivals Genoa respectively on Sunday.
