While Vietnam were losing to the Japanese in Hanoi, events in the south of the country helped to turn despair to joy at My Dinh National Stadium as Qatar's 2-1 defeat to United Arab Emirates in Ho Chin Minh City sent the Asian Cup co-hosts through to the quarter-finals.

"This is very good for Vietnam football and a very good achievement for the national team," said Vietnam coach Alfred Riedl after learning what had happened in the other game.

"Only a few people could have expected this result. We are very happy about this, of course."

The Austrian, who is in his third spell as Vietnam head coach, had been banking on a positive result from Ho Chi Minh City, having expected little from his side's own game against the Japanese.

"Before the game, I thought the bigger chance to advance to the quarter-finals would be the result from the south," he said.

"In the north, our match, our chance of getting a point was small. But in the south, anything was possible."

His prayers would be answered when UAE turned around a half-time deficit to defeat their Gulf rivals.

"I'm happy because they (UAE) did something," he said. "They were behind 1-0 according to my information but they continued working to make it a draw and even to win the match."

For a short while, it appeared that Vietnam would determine their own progress to the quarter-finals as they took a shock early lead in Hanoi following an own goal by Keita Suzuki.

But a brace by Seichiro Maki and further goals by Yasuhito Endo and Shunsuke Nakamura secured an emphatic win for the Japanese, who are chasing a third straight title and fourth overall.

"You've got to cope with any situations in this type of game. Our players were nervous early in the game when our opponents came out aggressively," said Japan coach Ivica Osim.

"I won't call it lucky but we were able to catch up with them in the early minutes of the game, which was good.

"Our players soon found out what Vietnam tactics were. That's how we recovered. They did that on their own."

Japan claimed top spot in Group B and will remain in Hanoi to face Australia in the last eight on Saturday while Vietnam will travel to Bangkok to take on Iraq on the same day.