Bridges suffered their worst ever defeat since joining the Ryman League on a ground where they crashed 5-1 only last season.
Merstham looked pacey from the start but Bridges had the best chance of the first half hour when John Lansdale shot over after a neat lay-off by Tony Garrod, who had been an early replacement for the injured Allan Tait.
But Merstham were gaining a lot of free-kicks in dangerous positions, and three minutes before half-time Tutu Henriques lost his marker to head home from Fabio Saraiva’s free-kick.
And two minutes later Merstham doubled their tally when a throw down the left by Simon Cooper was nudged on for Aaron Rhule to net cleverly with an angled shot into the far corner past stand-in keeper Tom Fawdry.
Bridges had an encouraging spell early in the second half without really looking like scoring and the introduction of Taurean Roberts and Stefan Cox from the Merstham bench after 65 minutes proved crucial.
Within two minutes, Cox’s pace led to him setting up a simple chance for Roberts, and after 73 minutes Roberts had another easy tap-in after defensive mistakes.
Roberts completed his hat-trick after 81 minutes as he created the opening for himself, and as the game entered five minutes of added-time, when no-one met a low cross in the home goalmouth, the ball was swiftly sent to the other end for Omar Folkes to meet Elliott Thompson’s well-worked cross for an embarrassing sixth goal.
Bridges: Fawdry, Peauroux, Leach, Brake, MacVicar, Lansdale (Pulling 73), Crellin, Carney, Godfrey, Tait (Garrod 10), Daniel (Roberts 63). Unused subs: Djimah, Morey.
Aerotron Man of the Match: Nigel Brake