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The strike made him the oldest player to score 15 goals in a Serie A season, at 39 years and 169 days, and sounded the starting gun to a frantic encounter in Florence.
The Swede needed only nine minutes to fire home the opener after springing the offside trap in his first league appearance since picking up a muscle injury against AS Roma on Feb. 28.
Milan moved up to 59 points in second place but Inter have a game in hand after their match against Sassuolo was postponed following a cluster of positive tests for COVID-19.
Fiorentina remain 14th with 29 points, seven clear of the relegation zone.
"I feel young, don't talk about age. The more time passes the younger I feel," Ibrahimovic said. "I'm taking responsibility, helping on and off the pitch. Today I played the whole game, it's an intense moment."
AC Milan manager Stefano Pioli said his players needed every ounce of remaining energy to earn the win and was pleased to hear Ibrahimovic had targeted the title in his post-match interview.
"Ibra is right to talk about the Scudetto," Pioli told Sky Italia. "We must try to win all our games, our future depends on us and we have the qualities to try and win every single game. They will all be difficult.
"We started out with different objectives, but now we are up there. We have broken a lot of records, but if we don't do well in the next few games it won't lead to anything.
"There are seven very strong teams, four of them will be happy [to qualify for the Champions League] at the end and three less so."