Holders Singapore beat Indonesia to win group
Baihakki Khaizan gave the Lions the perfect start with a first-minute goal which stunned the crowd of 50,000 in Jakarta.
Si Jia Yi doubled the advantage five minutes after the break to seal Singapore's third win from as many matches.
Despite the defeat, Indonesia went through to the semi-finals as the group runners-up, three points behind Singapore and ahead of Myanmar and Cambodia.
Indonesia are most likely to meet three-times champions Thailand in the final four, if the latter avoid defeat against second-placed Malaysia in their final Group B match on Wednesday.