Holders Japan stormed into the Asian Cup quarter-finals with a clinical 4-1 demolition of co-hosts Vietnam on Monday.

But Vietnam, appearing in the tournament for the first time in 47 years, joined Japan in the last eight after Qatar lost 2-1 to United Arab Emirates in the other Group B game.

"I'm still not satisfied," Japan coach Ivica Osim told reporters. "If I was satisfied then I might as well just quit as coach."

Japan's reward for finishing top of their group is a grudge quarter-final against Australia, who avoided an early exit with a 4-0 win over Thailand in Bangkok later on Monday.

A Keita Suzuki own goal put Vietnam ahead after just seven minutes and triggered riotous celebrations among a crowd of 40,000, but it took Japan just five minutes to restore normal service.

Celtic midfielder Shunsuke Nakamura found space on the left to float over a perfect cross for Seiichiro Maki, who had the simple task of chesting the ball into an open goal.

Yasuhito Endo put Japan ahead just after the half hour, rifling a free kick into the top corner from the edge of the box to briefly silence Vietnam's trumpet-blowing fans.

Nakamura added a third seven minutes into the second half with a superb right-foot strike before Maki headed in his second from close range in the 59th minute.

Maki told Reuters Japan were happy to get the opportunity to avenge their 3-1 defeat by the Socceroos at last year's World Cup in Germany.

"If we'd have a choice of opponents, Australia would have been first on the list," he smiled. "That's the team we wanted to meet and have the chance to bury those ghosts."

When news of UAE's win over Qatar in Ho Chi Minh filtered through, Hanoi's My Dinh stadium erupted in a deafening roar as Vietnamese fans began to celebrate wildly.

"It's a sensation," beamed Vietnam coach Alfred Riedl. "Nobody expected us to be in the quarter-finals. It's the first time Vietnam's history.

"I'm extremely proud of my players and maybe Vietnam will surprise again."

Japan, bidding for a third straight title, finished top of Group B on seven points with Vietnam runners-up on four. UAE were third on three points with Qatar on two.

Japan play Group A runners-up Australia in Hanoi on Saturday, while Vietnam travel to Bangkok to face Iraq.