Vietnam's win promotes them from Group C to the quarter-finals.
It was Vietnam's fourth win in a row at the tournament.
Coach Mai Duc Chung made changes to the starting line-up.
Midfielder Tran Thi Thuy Trang, wingback Vu Thi Nhung and striker Nguyen Thi Minh Nguyet started from the bench.
Improvementsto the team's overall fitness, playing against a weaker opponent andwith group advancement on the line, Vietnam quickly asserted control tocontain the play to Hong Kong's half.
Within four minutes, Hong Kong defender Wong So Han delivered Vietnam's first notch on the scoreboard.
Nhungsprinted forward to take up a loose ball left for grabs, forcing Wonginto a rushed attempt at clearing the ball, inadvertently heading theball into her goalie's net.
Vietnam's attack became livelier with the early lead.
Nguyen Thi Tuyet Dung doubled the advantage with a penalty conversion after teammate Nguyet was fouled by He Ying in the box.
HongKong ventured forward in search of goals, but it took 38 minutes tofind a real chance when Wong Shuk Fan's close range rebound was blockedby Vietnamese goalie Dang Thi Kieu Trinh.
The 38th minute was theonly real threat Hong Kong posed to the Vietnamese goalkeeper, whospent most of the first half watching her teammates dominate the far endof the pitch.
Another penalty was awarded to Vietnam's NguyenThi Muon after she was fouled in the box. Dung once again took the kick.Her effort was promptly met by Hong Kong goalie Leung Wai Nga but thereferee granted a retake after Hong Kong players encroached the penaltybefore Dung took the shot.
Second time around, defender Nguyen Thi Xuyen gave Leung no chance with a rising shot to the far high corner of the goal.
HongKong put their heart and soul into the game after the break, but theysimply could not match the Vietnamese side both in quality and tactics.
Hong Kong conceded two more goals to second-half substitutes Minh Nguyet and Pham Hai Yen.
Vietnamwill face familiar but tough foes, Thailand, in the first quarter-finalmatch on September 26 at the Namdong ASIAD Rugby Field.
The convincing win on September 23 sent a warning message to Thailand who have often come out on top in recent match-ups.
In their latest meet, Thailand beat Vietnam 2-1 in a World Cup play-off match in Ho Chi Minh City in May.-VNA