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Gravesend lost their grip on the game at Civil Service in their National League 3 London & South East mid-table match.
Gs had a commanding lead at one stage, but let victory slip from their grasp after conceding a couple of tries in the latter stages.
Despite losing the match 27-25 Gravesend did pick up a couple of bonus points to keep themselves safely in seventh position.
Service scored the opening try of the match but it was all-square when Ian Harman sprinted over the line.
Terry Papworth raced in Gs second try, with Dave Dorton converting and then adding a penalty soon after to move them into a 15-5 lead.
Service replied with a try of their own but Jamie Gwynne collected Gary Gray's chip to run over another try to lead 20-15 at the break.
Gs soon added another five points when Tom Bishop chased home for a touch-down, but it was to be Gs' last score.
Two tries for Service, one converted, turned the game on its head and handed the home side the victory.