The victory, which snapped Sos back-to-back losses to tough, more experienced rivals, hiked the 12-year-old Filipino whiz output to five points for a share of 25th place heading into the final round of the event.
Sos last round opponent is Indias Gupta, who in 2002 won the Indian National Junior chess crown at age 13.
A victory over Gupta will guarantee So his first IM result since he would fall in the Category VI (2376-2400) bracket, having a 2387 category rating average.
Meanwhile, GMs Gabriel Sargissian and Tigran Petrosian of Armenia and Ukrainian Sergey Fedorchuk share the lead with 6.5 points.
Fedorchuk drew with Petrosian in just 10 moves of Sicilian-Dragon encounter while Sargissian halved the point with top seed GM Zviad Izoria of Georgia after 19 moves of English Opening.