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.
"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."
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.
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.
