Leicester City midfielder Hamza Choudhury’s free kick put Bangladesh ahead after 13 minutes, much to the delight of the capacity home crowd at Dhaka’s National Stadium.
The SAR found their equaliser in first-half stoppage time, thanks to a close-range header from Everton Camargo.
Merkies capitalised on a costly Bangladesh mistake to score his first of the match in the 50th minute and put coach Ashley Westwood’s men 2-1 up.
Hong Kong doubled their advantage midway through the second half when Camargo slipped a simple pass from the right to Merkies, who slammed the ball home for his second goal.
But the home team wouldn’t go down without a fight.
Shekh Mosalin pulled one back for Bangladesh in the 84th minute, before Shamit Shome eventually drew them level in the nine minutes into stoppage time – sparking scenes of jubilation across the stadium.
But just two minutes later, Merkies capped off a spectacular hat-trick by lashing home the winner in the 101st minute to snatch victory for Hong Kong, China in spectacular fashion.
The result lifts the SAR squad to the top of Group C with seven points, two ahead of second-placed Singapore.
India are third while Bangladesh remain at the bottom of the table.
