Urbiztondo hit a three-pointer to tie the count at 77-all then Quinahan eluded defender Allan Gamboa for the go-ahead basket in the last 15 seconds.
The loss came as a shock for Harbour Centre which formed a star-studded lineup in a bid for a third straight championship in this tourney.
Reed Juntilla made a grand return to Dazz ‘Sang Patak team, going 5-of-5 from the three-point area and finishing with 27 points as the Kitchen Specialists beat the Toyota Balintawak side, 86-81, in overtime earlier.
Philip Butel scored eight points, including a follow-up on a miss by Juntilla with time down to 33 seconds, helping clinch the win for the Kitchen Specialists.
Dazz, which finished a surprise second in the Silver Cup, outscored Toyota Balintawak, 8-3, in the extra five minutes.
"Juntilla made great baskets in the fourth but I have to credit to Butel for a job well done," said coach Jun Noel. "It’s a good win although nangangapa pa kami."