All five of Lausanne's prior league phase goals this season had been scored before half time, so an underwhelming and goalless first half spelt trouble for the home side.
Even the disruption of heavy fog descending on the Stade de la Tuiliere did little to alter the first half viewing experience from the stands, with moments of genuine excitement scarce.
Of the rare opportunities on offer, the majority fell to the Swiss side, but neither Sekou Fofana nor Theo Bair could find the incisiveness needed to open the scoring. An audacious backheel by Bair released the onrushing Fofana, but the full-back wildly lashed his shot high and wide from a difficult angle.
Ten minutes later and Bair’s tame finish from eight yards out, after meeting a cross from the right wing, squandered the best chance of a tight opening 45 minutes.
A more vibrant showing from the hosts in the second half led to them deservedly taking the lead just shy of the hour mark, in a move started by Enzo Kana-Biyik twisting and turning his way to the byline.
The on-loan Manchester United man then stood up an exquisite cross to the back post, which the arriving Sigua nodded home beyond Tommaso Martinelli in the Fiorentina goal.
A fragile and despondent Viola were once again spiralling, with Beyatt Lekweiry allowed to run hassle-free into the Italian’s box, but the Mauritanian was impressively denied by an outstretched Martinelli.
It may not be enough to save Paolo Vanoli his job, but a late rally meant Fiorentina left Switzerland with at least some respect intact, as smart saves from Karlo Letica condemned them to another defeat and a 16th-placed finish in the league phase.
Flashscore Man of the Match: Beyatt Lekweiry (Lausanne)