The knockout stage was the second and final stage of the 2018 AFF Championship, following the group stage. It was played from 1 to 15 December with the top two teams from each group (two in total) advancing to the knockout stage to compete in a single-elimination tournament. Each tie was played on a home-and-away two-legged basis. The away goals rule, extra time and penalty shoot-out were used to decide the winner if necessary. Vietnam won 3–2 on aggregate against Malaysia in the final to win their second title.