Forest Green were relegated from the Blue Square Premier in dramatic fashion as Grays fought back to claim victory.
Following an uneventful first half, Reece Styche was brought down in the area and David Brown converted the penalty to give Forest Green the lead.
Despite piling on the pressure Forest Green could not finish the game off and Alex Osborn drew Grays level with a well taken finish.
Alsseny Cissoko headed home a late corner to send Forest Green down.
In a goalless first half it was Grays who had the best opportunities, with Cissoko seeing an early close-range header blocked by Forest Green keeper Mark Preece.
Rovers went into the lead just after the hour when Harlee Dean fouled Styche in the area, Brown confidently converting the penalty.
Despite having more possession and chances, Forest Green were pegged back when Osborn scored from the edge of the area.
With a draw enough to keep Forest Green in the Blue Square Premier they seemed to have done enough until Cissoko headed home an Alex Rhodes delivery four minutes from time to sink Dave Hockaday's side.
Grays Athletic manager, Julian Dicks told BBC Essex:
"The ground is closing so it was important we went out on a high, obviously it hasn't been the best of seasons.
"The last three games we got seven points, it is a shame we couldn't do that a few games earlier.
"I just told the lads to go out there and win, and they did. If they want me I'll stay at Grays."
Forest Green boss Dave Hockaday told BBC Radio Gloucestershire:
"Second half I thought we were excellent, scored a goal and missed some absolute sitters and then, maybe typical of our season, from absolutely nothing an individual mistake has given them a lift and a goal."
"I'm devastated, I'm gutted for my players, for the fans, for the board and the chairman."
"I can't ask any more of my players effort-wise, we weren't clinical enough because we've had some absolute stonewall sitters, it's a tough day."
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