The Laotians took top spot in the qualifying competition with nine points after downing last-placed Timor Leste 2-1.
Lamnao Singtao blasted Laos in front after seven minutes and Visay Phaphouvanin extended their advantage from close range five minutes after the interval before Timor Leste captain Alfredo Esteves pulled a goal back in the 64th minute.
Hosts Cambodia booked their berth after coming from behind to beat Brunei by the same score.
Hardi Anak Bujang fired Brunei ahead in the 44th minute but Sam El Nasa tucked away a rebound a minute later to send the sides in level at half-time.
Borey then delighted the crowd of 15,000 when he fired past Mohammed Wardun Yussof 17 minutes from time to give the Cambodians all three points.
Cambodia and the Philippines finished tied on points and goal difference but the Cambodians advanced, having scored more goals in their four games.
In the Suzuki Cup in December, Cambodia will face defending champions Singapore, Myanmar and hosts Indonesia in Group A while Laos will play Vietnam, Malaysia and hosts Thailand in Group B.