HAGL conceded two goals in the first 25 minutes to their much better opponents.
Brazilian striker Leo Ceara, 27, authored both goals from set pieces, partly thanks to poor judgement by Vietnamese keeper Tuan Linh.
But HAGL did not go down easily. They were offensive from the start of the game, but Van Thanh's early shot inside the box hit the post.
Five minutes after losing the second goal, they created a struggle that forced Yokohama’s keeper Takuya Kida to score an own goal.
In the second half, they had three corners that threatened the opponents’ goal, but poor performance by foreign players, Brazilian Washington Brandão and Jefferson Baiano, stopped them from making any real changes.