Lock Anthony Bush scored the late try which secured a double triumph for Old Brightonians.
The Sussex Three champions added the Junior Plate to their trophy collection with a 10-7 win in the final over Ditchling, the side they also pipped to league honours.
Ditchling looked to have played it to perfection in an enthralling tussle at Hellingly.
They put great faith in their heavier pack and tactical kicking, as well as defending superbly after Mark Pratt had claimed a pushover try to put them 7-0 up.
Mike Edmunds replied with a penalty but strong running from Adam Phillips and Tom Howell was unable to break through the Ditchling tacklers.
In the end it was a forward drive which clinched victory as Bush got over at the posts and Edmunds converted.
OBs stalwart Peter Rumney said: "The tone was set in the opening minute when Ditchling shoved us back at the first scrum.
"Our players were very excited at the end and Hellingly made sure it was an enjoyable day all round with their organisation."
Ditchling's Tom Clarke admitted his team were shattered but added: "It was an entertaining and exciting contest."
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