Bustamante whipped Marcos Castro of Costa Rica, 5-1, and Shawn Budd of Australia, 5-2, in Group 7 action last Saturday but failed to notch a third straight victory when he dropped a 2-5 decision to Thomas Engert late last night.
Corteza survived Rico Diks of Holland, 5-4, and Darren Appleton of England, 5-3, on opening day and followed it up with a 5-1 victory over Luis Miguel Sanchez of Venezuela.
Gallego, who topped his group last year before losing to American veteran Earl Strickland, 8-9, in the round-of-64, made the biggest noise Saturday by being the only player in the field to win two matches without yielding a single rack.
Gallego posted similar 5-0 victories over George Sarmas of Greece and Brian Naithani of Germany. His third victory came at the expense of Wayne Lloyd of Wales, 5-3.
Winning in the afternoon matches Sunday were Rodolfo Luat over Mark Williams of Wales, 5-4, and Warren Kiamco over Frankie Hernandez of the US, 5-3.
Efren "Bata" Reyes, the 1999 world champion, made short work of Niklas Bergendorff of Sweden, 5-2, and Alok Kumar of India, 5-0 in Group 5 action Saturday. He and the rest of the Filipinos were scheduled to play two games each Sunday.
The tournament offering a top prize of $65,000 drew 128 players divided into 16 groups of eight players each. They will play a single-round robin, race-to-5 eliminations with the top four from each group making it to the round-of-64.
The round-of-64 will be a race-to-9, winner-breaks affair leading to the next round to be played under the same format. The round-of-16 will be a race-to-11 en route to the quarterfinals and the semifinals. The finals on July 21 will be a race-to-17.