Cheered by a small but loud Filipino supporters, del Rosario, who made it here on the strength of a second place finish in the Manila leg last June, capped a sterling game with five straight strikes in the final five frames to boot out Chai and arrange a semis duel with another Malaysian Shalin Zulkifli.
"I had a hard time adjusting but I kept my cool until my game came," said del Rosario, whose semis foe Zulkfli, who owned the events game-high of 299, downed countryman Choy Poh Lai, 211-171.
The player-coach tandem of Chester King and Purvis Granger likewise moved into the next round, hurdling their respective assignments to clinch RPs first semifinal appearance in mens division in Tour history.
Picking up the pace early, King unleashed a five-bagger and never looked back to smash Australian Andrew Frawley, 232-182, while Granger, an American coaching in RP for two years now, survived a serious challenge from Korean Yoon Dal Young to escape with a 203-202 win.
"I started out hot and that I think was the key to this win," said King, the Hong Kong leg winner.
King and Granger, the Manila leg champion, however, part ways as the two clash in the Sundays semifinals.
Guams Duane Camacho, a first-timer who has Filipino ancestry, pulled a king-sized upset, stunning elimination round topnotcher and Busan Asiad triple gold medalist Remy Ong of Singapore, 212-202.
Next stop for the power-bowling Camacho, who trained in the Philippines under national coach Johnson Cheng and Granger, is Thai wonder Teerapol Sajjaktrakul, who trounced Chinese Taipei leg winner Zalmazran Zulkifli, 205-189.
The other womens semis pairing pits Korean Koo Hyun Jee, winner over Tour veteran Yap Seok Kim, 236-215, versus elims leader Malaysian Lai Kin Ngoh, who waylaid Japanese Hiroko Shimuzu, 242-146.