Still unbeaten this season, second-placed Juventus stayed four points behind AC Milan after the leaders won 2-0 at Parma with a Zlatan Ibrahimovic penalty and a brilliant solo goal by Urby Emanuelson.
Milan, who brought on Gennaro Gattuso late in the game for his first appearance since suffering an eye problem in September which led to speculation he may have to abandon his career, have 60 points from 28 games.
Club president Silvio Berlusconi was among the crowd for Milan's fourth successive away win.
"The presence of the president away from home was a good sign. When he's here there's more motivation to do well," said coach Massimiliano Allegri.
"He's happy with the performance and with the win. The players played a good game and when it was time to grit their teeth they did so."
Juventus had drawn six of their last seven games, allowing Milan to overhaul them in the process, but got off the mark in style at Fiorentina as Mirko Vucinic curled in an exquisite effort from the edge of the area after 15 minutes.
Six minutes later, Fiorentina had Alessio Cerci sent off for kicking Paolo De Ceglie off the ball and when Chilean Arturo Vidal scored a second for the visitors before the half-hour, it was all over as a contest.
Claudio Marchisio, Andrea Pirlo and substitute Simone Padoin were on target after the break as Juve chalked up their biggest win of the season.
Predictably, Fiorentina fans jeered their team in the second half. Their side are 15th in the table with 32 points, only seven clear of the relegation zone.
Milan were missing Robinho, Mark van Bommel, Kevin-Prince Boateng, Ignazio Abate, Clarence Seedorf, Alessandro Nesta and Alexander Pato for their visit to Roberto Donadoni's Parma, who are 17th with 31 points.
BRIGHT START
Parma started brightly with Sebastian Giovinco pouncing on a mistake only to fire over before Jaime Valdes ended a good run by shooting wide from the edge of the penalty area.
Milan won a penalty with their first real attack when Emanuelson's shot hit Cristian Zaccardo's arm and Ibrahimovic, Serie A's leading scorer, made no mistake from the spot as he fired his 20th goal of the season.
Parma's misfortune in front of goal continued as Gabriel Paletta's header bounced off Thiago Silva and struck the bar. However, Milan were creating plenty of chances of their own with Stephan El Shaarawy hitting the post.
Milan wrapped up the match in the 54th minute when Antonio Nocerino slipped the ball to Emanuelson on the counter-attack.
The Dutchman burst between two defenders, surged forward, slipped past goalkeeper Antonio Mirante and tucked the ball into the net for his second goal of the campaign.
Just to prove it was not Parma's night, Sergio Floccari struck the crossbar with a fierce volley in stoppage time.
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