Immonen topped Bustamante, 11-8, in the semifinals, then tripped Reyes, 13-12 , in the final of the four-day event featuring the cream of pool masters in the world.
Immonen earned $20,000 for his feat while Reyes pocketed $10,000 for his runner-up finish.
Reyes squandered a commanding 9-4 lead as he failed to duplicate his victorious stint in the recent All-Japan championship in Osaka.
His conquest of compatriot Leonardo "Dodong" Andam, a former SEAG gold medallist, and Finnish Mika Immonen in the semifinals and finals of the RP Open augured well for his stint in Vietnam.
Reyes advanced to the championship match with an 11-7 whipping of Andam early in the night.
Immonen averted what could have been an all-Filipino final as the one-time World Pool champion defeated Francisco "Django" Bustamante, 11-8, in their own semis duel.