The Germany international left it late to secure three points to keep the club's incredible winning Liga run going, after Fabian Orellana had levelled with a stunning shot.
Injuries to Jeremy Mathieu and Andres Iniesta put something of a dampener on the Catalans' victory in Andalucia.
CHICAGO — The Colombian fans were still standing near their seats more than 90 minutes after the Copa America Centenario semifinal between their Cafeteros and Chile was supposed to have ended.
The Argentinian netted a brace and Patrice Evra, Giorgio Chiellini and Leonardo Bonucci scored as Max Allegri's outfit ended another successful season on a high.
The hosts are already resigned to playing next season in Serie B, but they put in a stellar performance to down the champions after the former Italy international struck.
The home side found themselves down to 10 men after just 12 minutes as Amadou Diawara received two yellow cards, but it took a penalty to secure the win for the Rossoneri.
The striker hit the winner in a dramatic finish in Florence as the visitors moved 12 points clear at the top and will be crowed champions if Napoli fail to win at Roma on Monday.