Venuti left the field in tears after he deflected Juan Cuadrado’s cross into his own net in the first minute of stoppage time to hand Juve the win and a potentially crucial away goal.
Serbia forward Vlahovic was back at the Stadio Artemio Franchi for the first time since moving to Turin in January but had little joy for depleted Juve in a tense match which lacked quality.
The tie will be decided at the Alianz Stadium next month, with the winners taking on either AC Milan or Inter Milan — who drew 0-0 on Tuesday — in May’s final in Rome.
Fiorentina fans had promised a fiery welcome for former hero Vlahovic, whose departure to fierce rivals Juve for an initial 70 million euros ($80.2 million) brought an end to months of speculation around the 22-year-old’s future.
He had enraged Viola fans by refusing to sign a contract extension which owner Rocco Commisso said would have made him the highest-paid player in the club’s history.
Home fans made an enormous racket with the 10,000 whistles handed out creating a blistering noise, and the teams came out in front of a huge display depicting Medieval Florentine poet Dante surrounded by flames.
A banner directed at Vlahovic cited Canto 26 from ‘Inferno’, a passage from the eighth circle of Hell about the fate of enablers of fraud.
However, the high-culture barracking of their former player was debased by a large group of Fiorentina fans who ignored the club’s plea to not racially abuse Vlahovic, with chants of “you’re a gypsy” clearly heard during the pre-match warm-up.
With the match underway the players responded to a firecracker atmosphere with frenetic football lacking composure.
Juve had nine players absent, with Denis Zakaria becoming on Monday the latest in a long line on the treatment table alongside the likes of Paulo Dybala, Federico Chiesa, Giorgio Chiellini and Weston McKennie.
Fiorentina went closest in the first half when Jonathan Ikone set off down the field and bamboozled Mattia De Sciglio before dragging centimetres wide.
France international Ikone went even closer shortly after the break, curling a shot off the outside of the post after being sent bursting through by Lucas Torreira and again brushing aside De Sciglio.
Vlahovic’s only good chance, a miscued lob, was then tipped away by Pietro Terracciano in the 56th minute.
From there the match looked to be heading toward stalemate until the unfortunate Venuti gave Juve a goal which makes their passage to the final much more likely.