Following a disastrous World Cup elimination on home soil under Luiz Felipe Scolari, USA 94-winning captain Dunga has now guided the national side to four consecutive victories without conceding a goal.
Despite Dunga's criticism of the surface at the Singapore Stadium, skipper Neymar impressed throughout - seeing a free-kick hit the post shortly before sending Brazil in front.
Latching on to Diego Tardelli's pass, the lively forward took the ball round Eiji Kawashima before doubling his tally early in the second half when he finished one-on-one after a delightful through ball from Philippe Coutinho.
Japan - who ensured Javier Aguirre his first victory against Jamaica on Friday - were unable to respond as Neymar added two more late on.
The dominant victory rounds off a positive tour of Asia that saw Brazil clinch the Superclasico de las Americas against Argentina in Beijing on Saturday.
Buoyed by the 2-0 win over their fierce rivals in China, Brazil began brightly but were made to wait until Neymar's free-kick come back off the upright after 16 minutes for their first chance.
The Brazil skipper had seen a half-hearted penalty appeal turned down when he was eased off the ball by Masato Morishige prior to his set-piece striking the woodwork.
However, the Barcelona forward found the net shortly after when he timed his run to beat the offside trap and get on the end of Tardelli's pass before rounding Kawashima and calmly finishing.
Neymar continued to threaten - beating Tsukasa Shiotani all ends up only to see his effort drift wide - before Japan had their first sight of goal courtesy of Yu Kobayashi's volleyed effort that sailed over the crossbar after patient build-up down the left.
Shinji Okazaki's glanced header drifted wide of Jefferson's left-hand post as Aguirre's men ended the half strongly, despite the absence of playmaker Shinji Kagawa due to a head knock picked up against Jamaica.
However, Neymar's second just two minutes after the interval put the game beyond Japan - substitute Coutinho was the architect with his first real contribution of the game before the captain ran clear and rolled the ball past Kawashima.
Brazil, who gave a first start to Gil in the absence of injured defender David Luiz, then saw experienced midfielder Kaka hit the crossbar with a header as he was denied a first international goal in almost two years.
However, Neymar had his hat-trick when he followed up Coutinho's parried effort before nodding in Kaka's cross to ensure his and Brazil's fourth with nine minutes left on the clock.
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