Lorenzo Insigne scored twice in a lively Italy performance on a difficult, lumpy pitch, though there were question marks over the defence and third-choice goalkeeper Mattia Perin.
A capacity crowd of about 17,000 packed into the Raulino de Oliveira stadium in the steel town of Volta Redonda, providing fervent support for Fluminense and jeering Italy's Brazilian-born midfielder Thiago Motta whenever he touched the ball.
"We saw some interesting things and the two boys in attack did very well," Italy coach Cesare Prandelli told RAI television, referring to Immobile and Insigne.
The pair scored a goal apiece in the first half but Fluminense, second in the Brazilian championship, pegged Italy back each time through Chiquinho and Carlinhos, whose toe-poked effort slipped through Perrin's hands.
Immobile then netted twice in as many minutes soon after the break, the second a delightful flicked finish after he was sent clear by Thiago Motta, and Insigne made it 5-2 when he turned in Immobile's pass from close range.
Matheus Carvalho reduced the arrears with a long-range goal as Prandelli gave several first-choice players, including playmaker Andrea Pirlo and forward Mario Balotelli, a run-out in the final half hour.
Italy were held in a goalless stalemate with Ireland and suffered an embarrassing 1-1 draw at home to Luxemburg in their previous two friendlies. They face England in their World Cup opener in Manaus on Saturday before taking on Costa Rica and Uruguay in Group D.


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