The two sides were tied first in the group before the match, so whoever wins would be guaranteed a spot in Saudi Arabia while the loser would see their Asian Cup campaign end.
The SAR built a 1-0 lead at the break after a strong first-half performance but couldn’t hold on to it.
Backed by an energised home crowd, Hong Kong, China started pressing forward from the very beginning, creating chance after chance.
Their efforts paid off in the 15th minute when Everton Camargo swung in a perfectly placed cross to set up Matthew Orr for an easy header to break the deadlock.
Veteran goalkeeper Wang Zhenpeng – who was called up after first-choice Yapp Hung-fai suffered an injury against Bangladesh – put in an honourable performance, denying the visitors on several occasions.
But his efforts were not enough as Singapore equalised in the 53rd minute when Shawal Anuar chipped a stylish finish over the 41-year-old.
Hong Kong conceded another goal five minutes later.
Substitute Ilhan Fandi was left unmarked on the edge of the box and smashed home a stunner, leaving Wang with no chance.
The SAR pushed desperately for an equaliser in the final minutes.
The home team came close when Everton’s free kick deflected off Safuwan Baharudin and struck the crossbar.
The 2-1 defeat means Hong Kong now trail Singapore by three points and on head-to-head record, with just one match left.
Attendance was 47,752, a record for Kai Tak Stadium.
