Vincenzo Montella's side saw off their relegated hosts with ease thanks to a hat-trick from Adem Ljajic and goals from Steven Jovetic and Matias Fernandez.
Marco Vittiglio scored a consolation for the hosts, but there was no consoling Fiorentina at the final whistle as they discovered their efforts had been in vain.
A late winner for AC Milan at Siena meant it was they and not the Viola who took Italy's third berth in the Champions League, leaving Fiorentina the consolation of a place in the Europa League.
The visitors set about their task with gusto, needed only 15 minutes to go in front as Juan Cuadrado's low shot was tucked in by Ljajic.
Less than 10 minutes passed before Ljajic doubled the lead, latching onto Fernandez's through ball and finishing into the bottom corner.
The game was effectively over as a contest three minutes later when Fernandez shot low into the bottom left-hand corner from just outside the penalty area.
The one-way traffic continued in the second half with a lucky ricochet falling for Jovetic, who kept his cool to slot the ball past a helpless Mattia Perin.
Ljajic was then put through on goal and showed his customary composure to complete his hat-trick in the 58th minute.
Pescara grabbed a consolation when Togni's free-kick was only parried by Emiliano Viviano and Vittiglio converted the rebound.
However, with the win assured Fiorentina's hearts were broken by events in Tuscany.
Siena, who were holding Milan to a 1-1 draw, conceded with less than four minutes remaining to deny Fiorentina their place among Europe's elite next season.