Southport skipper Steve Soley could hardly have chosen a worse time to miss a penalty and his failure to convert the spot-kick left his side with just three points out of a possible 24.
The award was made in the 71st minute when the opposing captain Martin Foster handled a centre from Dean Howell deep inside the area.
Soley offered Robert Pell, who had scored both Southport goals, the chance to complete his hat-trick but Pell turned it down and Soley's kick hit the top of the crossbar on its way behind.
That proved to be the turning point as Forest Green proceeded to wipe out their deficit to snatch a draw, their second goal coming deep in stoppage time.
It was also a major disappointment for Pell who marked the start of his second spell with Southport with two superbly taken early goals.
The first of them came after play had been in progress for just 43 seconds he picked up a loose ball 20 yards from goal, went between Matt Russell and Darren Jones before firing past Steve Perrin from just inside the penalty area.
Southport had a goal disallowed shortly afterwards when Steve Pickord was ruled to be offside after firing past Perrin from close range.
Forest Green made their own contribution to the first half in the 12th minute when Alex Meechan took advantage of a mis-kick by Neil Moore, but his shot which had beaten Steve Dickinson rebounded to safety off the foot of a post.
Southport celebrated that escape by increasing their lead in the 18th minute with Pell again on target.
This time he saw a shot from a corner on the left by Howell cleared off the line by Foster, but the ball went back to him and he drove it home from ten yards.
Southport continued to dominate play and, all things considered, the visitors must have been glad to reach the interval only two goals behind.
Their manager Colin Addison made several tactical changes during the break sending on Steve Tweddle in place of Lee Russell and the sub played his part in a major improvement by his side.
It was their turn to cash in after Soley's missed penalty as they reduced the lead in the 76th minute, the home defence failed to clear a corner on the right by Gary Owers and Darren Jones beat the unsighted Dickinson with a shot from the penalty spot.
After that Southport were never able to regain their first-half standard and Jones equalised in time added on at the end.
This one came when Foster chipped a free-kick in to the penalty area and Jones climbed high to head home at the far post.