Franck Ribery rolled back the years but Fiorentina were stung by a late Inter rally as Antonio Conte's side snatched a thrilling 4-3 win to launch their Serie A campaign.
Former Bayern Munich winger Ribery created second-half goals for Gaetano Castrovilli and Federico Chiesa as Fiorentina looked set to take the points at San Siro on Saturday, only for Romelu Lukaku and Danilo D'Ambrosio to strike late on.
A dramatic game saw Fiorentina lead early on through Christian Kouame, but Lautaro Martinez scored a majestic equaliser in first-half stoppage time and Inter were in front thanks to a Federico Ceccherini own goal soon after the break.
Ribery then began to run the show, first teeing up Castrovilli after a joyous run down the left, and then when his defence-splitting long pass fed Chiesa.
But with seven minutes remaining, Fiorentina took Ribery off, and Lukaku bundled in an 87th-minute leveller before D'Ambrosio thundered in a back-post header to take all three points.