The TNT Tropang Giga gunner took advantage of the Mongolians going into penalty with 1:37 left to play, making his first charity before missing the second, leading to a crucial offensive rebound by Samboy de Leon and to Vosotros' winner with 1:34 to spare.
"I just shot it. Everytime I'm open, I shot it," he said. "We didn't give up and we gave our best."
The booming deuce capped off Vosotros' eight point performance to propel the Philippines to the final four.
Gilas will face the winner of the match between Japan and New Zealand in the semifinals of the men's division at 6:15 p.m.
Lervin Flores and the Philippine team advance.
De Leon added seven points, Joseph Eriobu had five, and Lervin Flores scored one.
Anand Ariunbold paced Mongolia with eight in the shocker as the world No. 6 exited the tournament.
Philippines 21 - Vosotros 8, de Leon 7, Eriobu 5, Flores 1.
Mongolia 20 - Ariunbold 8, Davaasambuu 6, Tsogt 4, Enkhbat 2.