Hilal Alhelwe hammered home his second and Lebanon's fourth in the eighth minute of stoppage time to move it level with Vietnam on points, goal difference and goals scored in the ranking of the best third-placed teams.
However, an earlier yellow card for Robert Melki gave Lebanon six yellow cards to Vietnam's five, meaning its second appearance at the tournament ends in the group stage, while Mohamad Haidar's late caution after the final whistle took its tally to seven.
Having suffered 2-0 defeats to Qatar and Saudi Arabia, Lebanon needed to win by four goals to guarantee a spot in the last 16. However, their hopes suffered an early blow as a goalkeeping error handed North Korea the lead through Pak Kwang-ryong.
George Melki levelled matters and Alhelwe completed the turnaround before Hassan Maatouk made it three from the penalty spot.
Alhelwe had the final say but it proved in vain with no time left for Lebanon to find the fifth it needed.