There was also controversy at Juventus who beat Cesena 2-0 to stay unbeaten and go top with the help of a hotly-disputed late penalty.
That match saw Juventus captain Alessandro Del Piero's frustrating season continue when he was taken off injured after just eight minutes of yet another substitute appearance.
Colombian Victor Ibarbo scored a superb individual goal to give Cagliari a 1-0 win at Catania, the Sardinians' first victory since Davide Ballardini became their third coach of the season.
Juventus lead the table with 29 points from 13 games, two ahead of AC Milan, who won 2-0 at Genoa on Friday, and Udinese, who beat Inter Milan 1-0 away on Saturday.
Serie A's two crisis teams clashed in Florence where the hosts this week fined Alessio Cerci and Andrea Lazzari for a late night out and Roma were still reeling from the Osvaldo incident, where he punched team-mate Erik Lamela after last week's defeat at Udinese.
"I feel bad as any player Roma player does and as any other coach would feel is this situation," said Roma coach Luis Enrique.
"We coaches go through these situations, when you don't get the results, the doubts start to build up."
Fiorentina, wearing black armbands in memory of former Brazil captain Socrates who played for the club for one season and died earlier on Sunday, were looking for their first win and goals under new coach Delio Rossi.
They were quickly on top after Stevan Jovetic was hauled back by Juan in the 15th minute.
The Brazil defender was sent off while the Montenegro international coolly converted the penalty in the 15th minute for his sixth league goal of the season.
ROMA RESPOND
Roma responded well but suffered another blow just before half-time when Alessandro Gamberini headed in Riccardo Montolivo's corner to make it 2-0.
The visitors went to pieces in the last quarter of an hour when Fernando Gago was dismissed for a sliding tackle on Jovetic in the 77th minute and Bojan Krkic followed nine minutes later for punching a goal-bound shot off the line.
Uruguayan Santiago Silva converted the resulting penalty as Fiorentina moved onto 16 points, one behind their ambitious but troubled opponents and whose coach Enrique can look forward to a torrid week.
In Turin, Juventus struggled to break down a defiant Cesena and lost Del Piero with a gashed forehead just after the hour.
It was doubly frustrating for the 36-year-old who had been brought on in the 56th minute, rather than in the last few minutes as his been more common this term under coach Antonio Conte.
Claudio Marchisio broke through in the 72nd minute with his sixth goal of the season but Cesena were livid about Arturo Vidal's penalty, which settled the match 11 minutes later.
Goalkeeper Francesco Antonioli punched away a cross but
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