This always looked set to be an awkward assignment for La Viola, who were missing several key players and had to contend with freezing temperatures and an uneven playing surface in Bialystok.
Jagiellonia almost capitalised in slapstick fashion after 10 minutes when Niccolo Fortini failed to clear a cross into the six-yard box at the first attempt, before his second effort cannoned off Kamil Jozwiak and flew just wide.
The hosts dominated possession ahead of the break, but they failed to work Fiorentina goalkeeper Luca Lezzerini, who was starting his first European game in 10 years in place of the injured David de Gea.
It took until the 39th minute of a low-quality first half for either side to register a shot on target, when Giovanni Fabbian hooked a volley straight at Slawomir Abramowicz.
The Fiorentina midfielder went close again with a half-volley in first-half stoppage time, drawing an excellent diving save from Abramowicz, before Robin Gosens headed wide from the resulting corner.
Fiorentina remained in the ascendancy after half-time and took a deserved lead in the 53rd minute, when Jacopo Fazzini swung a cross to the far post and captain Luca Ranieri squeezed a header past Abramowicz from a tight angle for his third goal of the season across all competitions.
That moment finally sparked the game into life, and Fortini should have made it 2-0 when he danced through the home defence, only to be denied by Abramowicz, shortly before Alejandro Pozo saw a goal ruled out for offside and Bartlomiej Wdowik curled a free-kick against the post as Jagiellonia twice went close to equalising.
The visitors regained control with a moment of pure quality in the 66th minute, as Rolando Mandragora curled a free-kick into the top corner from 20 yards to score his seventh goal of the season across all competitions.
Roberto Piccoli then made it 3-0 nine minutes from time after he was fouled by Dawid Drachal in the box, firing the subsequent penalty into the top corner to take his goal tally for the campaign to six.
Jagiellonia pushed for a late consolation to take into next Thursday’s second leg in Florence, but Fiorentina kept them out to claim their fourth successive win on Polish soil in convincing fashion.
La Viola have now won three of their five away matches across all competitions in 2026 (D1, L1), while their opponents are left to reflect on only their third defeat in their past 10 competitive home matches (W7).
Flashscore Man of the Match: Rolando Mandragora (Fiorentina)
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