The 13-year-old Dandan, who started to compete in the 16-under and 18-under divisions after winning the 14-under title in the Coca-Cola Open in Subic last May, set up a second-round meeting with Roderick Lazaro, who rallied past qualifier Menardo Econg, 3-6, 6-1, 6-4.
Fifth seed Korean Lee Chang Hoon trounced wild card Julius Kraut, 6-2, 6-3, while compatriot Chung Eui Hyun downed Edu Manzano, 6-2, 6-4.
In other matches, seventh seed Jesse Lapore downed Renato Oligo, 6-0, 6-4, to advance against qualifier Garizaldo Caabay, who beat Australian Jimmy Tucker, 6-4, 6-3.
No. 8 Pop Sabandon, No. 10 Cris Cuarto, No. 11 Nino Salvador and No. 13 Luisito Clores also gained second-round slots in this event presented by Dunlop and Accel with support from Coca-Cola, San Miguel Corporation, PBCOM, Photokina, Equitable-PCI, PVL Restaurant-Little Lawrence, Copacobana, Trans Asia Power and The Philippine STAR.
Sabandon, a former RP Davis Cupper, scored a 7-6 (2), 6-1 victory over Allan Alfafara while Cuarto, a member of the RP team coaching staff, defeated Chase Tinio, 6-1, 6-4.
Salvador, the star player of the San Sebastian varsity team, outclassed qualifier Dindo Almeda, 6-2, 6-2 and Clores struggled past Beeyong Sison, 6-2, 7-6 (4).
In the doubles, top seeds Johnny Arcilla and Michael Mora III defeated Elberto Paglalunan, 7-5, 6-1, to lead the first-round winners.
Also advancing were second seeds Jesse Lapore and Rolando Ruel, who beat Conrado Amita and Zack Purugganan, 6-0, 6-2, third seeds Beeyong Sison and Junjun Toledo, who blasted Joseph Arcilla and Jandrick de Castro, 6-0, 6-0, and fourth seeds Joseph Victorino and Alexander Lazaro, who won over Rolly Anasta and Benjie Contado, 6-2, 6-3.