The midfielder netted a rare goal after 34 minutes when his curling effort from 30 metres went in off the post.
Forward Alberto Gilardino grabbed the second on the rebound eight minutes from time to settle a bad-tempered encounter and hand the Florence side their second win in eight league games. Alessandro Parisi pulled one back for Bari in stoppage time.
Fiorentina, who reached the Champions League round of 16 last season, have since been beset by a series of problems.
Their form tailed off at the end of the campaign and long-time coach Cesare Prandelli left to manage Italy, with new boss Sinisa Mihajlovic hampered almost immediately when forward Stevan Jovetic was ruled out for six months with knee trouble.
Other injuries and a lack of quality recruits in the transfer window contributed to their poor start this term while the club's owners have clashed with fans and fallen out with the city council over a new stadium.
Striker Adrian Mutu was supposed to offer a ray of light next Friday when his nine-month drugs ban ends but the Romanian is now being investigated by police over an alleged assault in a bar and Fiorentina have vowed action if he is found guilty.
