Relegation was finally confirmed as Bridges somehow contrived to lose a game that for long periods they dominated.
Apart from a couple of half-chances for Walton, Bridges certainly had the upper hand in a first half that incredibly finished goalless.
Jim Fenlon cleared a Tony Garrod shot off the line and Max Fitzgerald cleared another Garrod effort, while a close-range effort by Oneil Odofin was somehow cleared off the line in a packed goalmouth.
Garrod almost reached a peach of a through-ball by Dan Mobsby, Hakeem Adelakun was on target with a header and the half finished with keeper Denzil Gerrar making a good save to deny Dominic Toussaint.
The game was played at Merstham FC after vandals damaged the pitch at Jubilee Field.
Walton could only improve in the second half and Martin Grant was called upon to smother a decent effort on the turn by Moses Ashikodi.
After 59 minutes Jordan Cheadle saw a free-kick crash against the post.
His luck was out on that occasion but a minute later he took another free-kick which deflected off Lee Hall and looped over Martin Grant for an undeserved lead.
Abu Touray hit the outside of the post three minutes later, but the ball swept to the other end of the pitch for lively substitute Luke Holness to set up Sol Pinnock, who curled home with ease.
Garrod and debutant Ristel Benz Salomon had chances to reduce the deficit before Grant brilliantly tipped over another Cheadle free-kick in the 75th minute.
But Cheadle's resulting corner found an unmarked Gabriel Odunaike for a simple header to put Casuals incredibly three goals clear.
Kieran Allen-Djilali gave a lively substitute appearance and made the opening for Odofin to jab over the line after 78 minutes, and who knows what might have happened had Garrod made the most of a one-on-one just a minute later.
Garrod did get on the scoresheet with a delicious finish from Alex Rose's long ball with just two minutes remaining, but the Bridges hopes of a dramatic finale were dashed within 20 seconds as a long ball from Fenlon found Odunaike with the former Crawley Down favourite making no mistake.
There was still time for Odofin to head just wide from Touray's cross, but Bridges were left to rue not punishing Casuals in that dominant first half.
Bridges: M.Grant, Lansdale (Allen-Djilali 76), Rose, J.Grant, Mobsby, Odofin, Toussaint (Benz-Salomon 68), Hall, Garrod, Adekakun, Touray
Aerotron Man of the Match: Lee Hall