Striker Naohiro Takahara scored twice as Japan rebounded from a disappointing 1-1 draw with Qatar in their opener to go top of Group B on goal difference above co-hosts Vietnam.
"It was so hot that it was hard to play... 45 minutes was difficult enough," Japan's enigmatic Bosnian coach Ivica Osim told reporters.
"But obviously the ball never gets tired. It was important that we had about 95 percent of the possession and just wore UAE down by controlling the tempo."
Takahara, who played despite suffering from a fever he picked up on the evening of the game, put Japan in front after 22 minutes with a powerful header.
The former Boca Juniors forward who now plays for Eintracht Frankfurt doubled Japan's lead five minutes later, volleying home from 20 metres for his third goal of the tournament.
Celtic midfielder Shunsuke Nakamura added a third goal from the penalty spot four minutes before halftime to kill off a game played in sweltering conditions in Hanoi.
UAE's plight went from bad to worse to worse when Basheer Saeed was sent off for a nasty foul on Keita Suzuki eight minutes into the second half.
The Gulf Cup holders managed a consolation goal in the 66th minute through Saeed Al Kaas but it came too late to prevent them becoming the first team eliminated from the Asian Cup.
"I lost two kilos just watching because of the heat," said UAE coach Bruno Metsu. "If you don't fight with every last drop against Japan you have no chance."
The Frenchman added: "Japan are the best team in Asia and they have the individual players who can turn a game."
Japan face Vietnam and Qatar meet UAE in the final round of Group B games on Monday. This year's Asian Cup is being staged jointly by Vietnam, Indonesia, Malaysia and Thailand.
