Shell-shocked Syston threw this game away after leading 31-20 with just five minutes left to play.
But Longton staged a remarkable comeback with two converted tries before repelling one last attack from their hosts at the death.
In a match which ebbed and flowed, Longton were slow out of the blocks, lacking urgency and tempo.
But they took the lead when flanker Sam Longstaff intercepted in his own half and ran to the line.
Syston came storming back with a try and a penalty but Longton’s number 8 Dan Smith burrowed over to make it 10-10 at half-time.
Longton regained the lead in the second half with a converted try from skipper Lee Brogan and a penalty from Grant Hallam to give them a 20-10 lead with under half-an-hour to play.
But Syston stepped up the pace to run in three converted tries to lead by 31-20.
Their tries on the day came from Ian Smith (2), Jamie Skerritt and Adam Nunney, with James Morgan adding a penalty and four conversions.
But Longton began to throw the ball around and Brad Eldershaw capitalised on a loose ball to dive over in the corner.
Longton gathered the kick-off and played with great patience and confidence, going through numerous phases and gaining territory before winning a penalty.
The kick to the corner led to a lineout, from which Craig Wilson and his pack marched Syston over the line for an amazing winning score which Grant Hallam converted for a 34-31.
To their credit, Syston refused to lie down, however, and they surged forward and won a penalty.
It was too windy to kick, though, and they turned the ball over trying to run it.