[2] De Guzman won the prestigious Asian Junior Chess Championship in 1981 held at Dhaka, Bangladesh where he was awarded an outright IM title.
[17] On January 9, 2010, de Guzman won the 10th Bob Burger Open conducted at the Mechanics Institute, San Francisco, California, USA where he scored 4.5/5.
[18] De Guzman won the 2004 Sacramento Chess Championship over the 4th of July weekend going undefeated and scoring 5.0/6 (4 wins and 2 draws).
[19] De Guzman won the 2010 Dolan Memorial International Chess tournament held in San Francisco, California on October 9, 2010.
[23][24] In 2015, de Guzman joined the 2nd Millionaire Chess Open held from October 8–12, 2015 and won by Super GM Wesley So of the US.