Seymour got over the line in a photo finish at Kings Park.
The Lions levelled late in the last quarter before a Jordan Zuccala tackle set up the game-winning goal just seconds before the final siren.
It was a brilliant fight back by the Lions which turned a four-goal quarter-time deficit into a seven-point victory.
Kicking into the wind, Seymour managed just one goal in the first quarter.
Shepparton United was well and truly on top, booting five goals in the blustery conditions.
But when the tables turned it was Seymour which took the advantage.
The Lions kicked four goals to the Demons’ nil to level the score at 35 points a piece at half-time.
The lead traded places twice before a goal from Max Jones helped Seymour level things up at three-quarter time.
United drew first blood just past the minute mark of the fourth quarter.
It looked like the Demons might have done enough until Mick Bradbury kicked his third to put the Lions back to within a point.
The ball looked slippery, locked up between the middle and half-forward for the Lions, and both sides struggled to control possession.
Seymour continued to surge forward eventually scoring a point to level the score.
Under pressure, United was forced to rush a behind and hand the Lions the lead.
The Demons made one last attempt to rebound into their forward line, but a lightning chase and crunching tackle from Zuccala saw United penalised for holding the ball.
It was a set shot for Zuccala, who went back to slot the winning goal with seconds left on the clock.
Score: Seymour 9.8 (62) d Shepparton United 8.7 (55).
Goals: M. Bradbury 3, M. Jones 2, H. McLean 2, J. Morgan, J. Zuccala.
Best: D. McLarty, J. Eager, B. Gregson, H. McLean, B. Tarran, J. Zuccala.
The Lions were outclassed by Shepparton United at home.
Seymour struggled to hit the scoreboard, scoring only halfway through the second quarter.
Trailing by 28 points at half-time, the Lions had their work ahead of them, but it wasn’t to be as Shepparton United continued its dominant run and extended the lead with three more unanswered goals.
Seymour was over-run in the last quarter, scoring just two points.
United kicked another four goals to run out 76-point winners.
Score: Seymour 2.4 (16) lt Shepparton United 13.14 (92).
Goals: M. Itter 2.
Best: H. Jones, D. Fisher, M. Quine, R. Allison, C. McCloy, T. Davey.