Three first half goals set the Viola on their way. Luca Toni, a David Pizarro penalty and Alberto Aquilani gave the hosts the perfect start. Reginaldo handed Siena hope, before Toni sealed the points.
Stevan Jovetic was back after a six week injury layoff, while David Pizarro returned from compassionate leave after the premature death of his sister in Chile.
Emiliano Viviano dropped the goalkeeping gloves to Norberto Murara Neto after a poor performance in last weekend's 4-2 defeat at Roma. Michele Camporese missed out through injury and joined suspended duo Juan Cuadrado and Ruben Olivera on the sidelines.
The Viola took a deserved lead on 16 minutes. Manuel Pasqual's cross was headed in at the far post by Toni. It was a centre forward's dream and put on a plate. Pegolo had started to come for the ball, but was left scrambling and given no chance.
The home side were awarded a penalty three minutes later when Felipe tugged Toni back in the area. Pizarro stepped up and squeezed the spot kick underneath Pegolo who had guessed the right way. The Chilean openly wept for his sister upon scoring in a very touching and emotional moment.
Emanuele Calaio forced Neto into a good save on the half hour, after heading Alessio Sestu's cross towards the near post.
Siena wasted a free-kick from a dangerous position before half time and were duly punished. Romulo rolled the ball across the box and Aquilani had the simple task to tap in after the Siena defence switched off.
The home side almost added a fourth at the start of the second period. Aquilani hurled himself at a Pasqual cross and missed connecting with a diving header by a whisker.
Fiorentina took their foot off the gas and Siena enjoyed a good little spell. Savic closed a Calaio shot down before the frontman could pull the trigger. An unmarked Vergassola was then allowed to head a Sestu cross across goal. The Viola defence was non-existent once again when Calaio scuffed a half-volley wide.
Aquilani was fortunate to escape a card after a coming together with Manuel Coppola. As the midfielder went down he seemed to headbutt the substitute in the midsection. The action went unpunished and the two shook hands.
Jovetic was withdrawn after largely being a spectator, but the Montenegrin will be glad to have got an hour of match time under his belt. Roncaglia and Siena's Neto picked up daft bookings which means they'll be suspended for next week's games.
Fiorentina fell asleep once more and this time paid for it with 20 minutes to play. Alessandro Rosina fed Reginaldo who stepped into the box to smash a consolation into the roof of the net, giving Neto no chance at his near post.
Toni killed the game off on 79 minutes with a carbon copy of his first goal. This time, Valero picked out the veteran hitman to nod home at the far post and notch his sixth of the season.
In another groundhog day moment, Siena replicated the first half penalty incident when Massimo Paci pulled back Mounir El Hamdaoui. The defender was dismissed after a second booking and Aquilani ballooned the resulting spot kick over.
Fiorentina: Neto; Rodriguez, Roncaglia, Savic; Romulo, Aquilani, Pizarro, (Migliaccio 72) Borja Valero, Pasqual; (Llama 65) Toni, Jovetic (El Hamdaoui 60)
Siena: Pegolo; Neto, Paci, Felipe; Angelo, (Sestu 19) (Reginaldo 60) Vergassola, Bolzoni, Rubin; Rosina; Calaiò, Larrondo (Coppola 46)
Goals: Toni 16, 79 (F) Pizarro pen 19 (F) Aquilani 45 (F) Reginaldo 70 (S)
Sent off: Paci 87 (S)