Seo Hyun-sook’s spectacular strike set the Koreans on their way after just two minutes with Lee adding the second just before half-time.
Lee then claimed another early in the second period and although the hosts pulled a goal back through Phan Thi Trang, Jang Sel-gi completed the scoring near the end to leave Vietnam still searching for their first point.
Korea Republic broke the deadlock in fine style just two minutes into the game when a corner came out to Seo and her drive from 25 yards out arrowed into the top corner.
Vietnam keeper Tran Thi Kim Thanh then did well to parry Choi So-mi’s header from another corner at the far post before Yeo Min-ji was off target from inside the six-yard box with a shot on the turn.
Choi Yoo-jung saw a long-range effort saved by Thi Kim Thanh before Korea doubled their advantage just before the interval.
Lee picked up the ball on the left edge of the box and drove towards goal before dispatching a low finish past the Vietnam keeper.
The second-half followed much the same pattern with Korea largely on top and Vietnam threatening only sporadically on the break.
Kim Jie-un headed wide from close range shortly afterwards when she should have scored but Korea grabbed a third goal in the 53rd minute when Lee dispossessed a defender in the box and her weak shot was enough to beat the Vietnam keeper.
The hosts reduced the deficit just after the hour mark when Thi Trang rifled home from 12 yards after a corner had found its way through to the forward.
Thi Kim Thanh then pulled off a good save to deny Choe after Kim had cut the ball back to the forward following a powerful run down the right and she was off target with a header from another Kim delivery shortly afterwards.
Choe fired disappointingly over the bar in the 76th minute when in a good position before Korea Republic did eventually notch a fourth goal three minutes from the end when Jang Sel-gi rounded off a neat passing move in the box by finding the top corner.