A Nikola Kalinic hat-trick in a 4-1 win over Inter Milan sent Fiorentina top of Serie A for the first time since 1999 as the early season title race was blown wide open on Sunday.
Inter, who have not won the scudetto since their treble-winning feats of 2010, had boosted their early-season scudetto hopes by racing to a 10-point lead over defending champions Juventus after winning their opening five games.
Juventus, who have won just one of their opening six games, were at risk of being left 13 points in arrears.
But Inter were trailing from the fourth minute after Josip Ilicic put Fiorentina ahead from the penalty spot and after Kalinic had completed his brace by the 23rd minute Inter defender Miranda saw red for tugging the Croatian from behind.
Ten-man Inter eventually pulled a goal back when Mauro Icardi picked up his own rebound from a free kick on the hour.
But Fiorentina stretched their advantage on 76 minutes, Kalinic completing his hat-trick after a superb one-two with Ilicic.
Thanks to La Viola's superior goal difference, they went top ahead of Inter, who also have 15 points, for the first time since February 1999, with Torino two points off the pace in third.
"The biggest satisfaction is seeing how well the lads played," said coach Paulo Sousa, who was quick to shoot down suggestions Fiorentina would aim to become title challengers this season.
"Let's be realistic. There are teams who have a lot more quality and who have invested a lot in players. We have to keep on fighting with the team we have."
Inter coach Roberto Mancini looked distraught from the opening minutes of the encounter, and was forced to admit to Fiorentina's superiority.
"The penalty at the start changed the whole game for us," Mancini told Mediaset Premium.
"On Ilicic's first shot we conceded the second goal and after Miranda's sending off the game was over.
"From two shots, we were three-nil down. We still have quite a few things to improve on. But I have to say well done to Fiorentina, who played well and had control of the game."
The chink in Inter's armour will give hope to Roma, the runners-up the past two seasons, and Juventus, who have won the past four league titles.
Roma, 5-1 winners over new boys Carpi on Saturday, sit in sixth at four points off the pace although Juve's 2-1 defeat at Napoli saw the champions slump to 15th place at 10 points off the pace amid their worst start to the season in decades.
Days before their Champions League clash away to BATE Borisov, Roma's win came at a cost with Edin Dzeko, Francesco Totti and Seydou Keita all ruled out for up to a month with injury.
Juventus were beaten finalists in last season's Champions League final having already secured their first league and Cup double in 20 years, but Massimiliano Allegri's side are stuck in a mini-crisis.
Juventus have struggled to adapt to changes enforced by departures and new arrivals in the summer and, crucially, have hit only six goals in six games, nearly half the tally of Roma (13), four fewer than minnows Chievo (10) and the same as newcomers Carpi.