Having been the benefactors of two decisions that went to the video review system, it was third time unlucky for Inter as the referee deemed Danilo D'Ambrosio had handled the ball in the sixth minute of seven added on, with Jordan Veretout eventually stepping up to slot home following a five-minute VAR check.
Luciano Spalletti's side had been 3-1 up seven minutes into the second half, when Ivan Perisic netted with Inter's own VAR-awarded spot-kick after Matias Vecino and Matteo Politano had cancelled out Stefan de Vrij's first-minute own goal.
But Fiorentina rallied, and after Cristiano Biraghi had a goal ruled out by VAR, Luis Muriel's stunning free-kick set up a grandstand finish, with Veretout keeping his composure in extraordinary circumstances to secure a share of the spoils in Florence.
The frantic pace was set inside 17 seconds – De Vrij only able to divert Giovanni Simeone's flick into the back of Inter's net.
Fiorentina's lead lasted just five minutes, Vecino prodding home from Radja Nainggolan's cross, with the goal standing following a lengthy video review.
And Inter's torrid start was forgotten by the 52nd minute – Politano arrowing a low strike into the bottom corner before Perisic sent Alban Lafont the wrong way from 12 yards after VAR was used to deem Edimilson Fernandes had used a hand to block a cross.
Biraghi's superb strike looked to have reduced the deficit, but VAR confirmed that Muriel had fouled D'Ambrosio.
Muriel atoned by drilling in a sensational free-kick, and Fiorentina's luck finally turned when D'Ambrosio was penalised for handball, and with a review ensuring the decision was correct, Veretout made no mistake.
What does it mean? Inter feeling the heat
Victories for AC Milan and Roma had put the pressure on Inter prior to kick-off, and Spalletti's third-placed side are just two points above their city rivals, and with no sign that the Mauro Icardi saga is coming to an end anytime soon, Gennaro Gattuso could well be smelling blood.
Fiorentina, meanwhile, sit ninth, two points off the European qualification spots.
Super-sub Muriel inspires comeback
Having been harshly adjudged to have fouled D'Ambrosio in the build-up to Biraghi's thunderbolt, Muriel looked like a man on a mission.
His free-kick was an exceptional strike that gave Samir Handanovic no chance, and his pace and energy helped propel Fiorentina forward in the closing stages.
D'Ambrosio falls foul of VAR
Having got away with an earlier VAR call, D'Ambrosio did not get so lucky late on. He moved his arm towards the ball, and despite his protestations that Federico Chiesa's attempted cross came too close to his body for him to react, the referee was not fooled.
Key Opta Facts
- In all the last eight encounters between Fiorentina and Inter in Serie A there have been three or more goals scored.
- Fiorentina have drawn all the three home league games in 2019 – two of these with the score of 3-3.
- Inter are the first side to score more than one goal away from home against Fiorentina during the first half of the match in Serie A this season.
- Matias Vecino scored his first goal in Serie A this season – his last one was back in May 2018 against Lazio.
Inter face Cagliari in the top flight on Friday, while Fiorentina have a Coppa Italia semi-final first leg against Atalanta coming up on Wednesday, before facing the same opponents in their next Serie A outing.