Mariano, needing two points in the last four rounds to clinch the third GM norm and become the countrys fifth grandmaster, decided not to force the issue against Aung despite having a slight advantage at endgame, settling to halve the point after 89 moves of their French game.
Then ranged against Villamayor in the afternoon match, Mariano played to a quick draw, opting to preserve his strength in the crucial final two rounds Friday of the tough double-round robin event organized by the Asean Chess Confederation to give Asian players a chance to earn international titles and ratings.
Mariano has 5.5 points, 1.5 points behind Vietnam GM Nguyen Anh Dung while Villamayor is in third with 4.5 points.
The 29-year-old Mariano needs only to draw his last two games Friday to complete the required 6.5 points for a GM norm and a title he had been chasing since 1994 when he ruled the Asian Juniors in Malaysia.
But he will have to do it against tournament leader and perennial tormentor Anh Dung and Mynmar GM Zaw Win Lay, whom Mariano, whose stint is sponsored by long-time chess patron lawyer Andy Gatmaitan, clobbered in the first round.