A yellow card originally given to the wrong player proved vital as the Royal Navy lost to Esher.
The Navy were 15-0 up when Will Scott was sent to the sin-bin, despite Brad Janes first receiving the card.
From there, Esher roared back into the game and ran out 20-15 winners at full-time.
The Navy's opening match of their pre-season ended in a 36-15 defeat to Cambridge University and the Senior Service were looking to bounce back in their annual fixture against Esher.
Last year's match saw the Navy run out 42-24 victors and they made a good start on a cold night in Hampshire.
Ben Priddey grabbed the opening try of the match after a period of intense Navy pressure.
They were soon further in front.
Quick hands across the line allowed Ben Chambers to crash over and the Navy were 1o-0 up at half-time.
Priddey crossed again to make it a 15-point lead at the start of the second half, but it all went wrong for the Navy from there.
Scott was penalised and the yellow card out, but to everyone's surprise, it was Janes who it was shown to.
Soon enough, the referee realised his mistake and Scott left the field but being a man down cost the forces team.
Esher scored two well-worked converted tries as well as two penalty kicks to out-score the Navy and win the game.