Seymour finished in front 12.5 (77) to 10.13 (73) when the final siren sounded.
Euroa started the better leading by 20 points at quarter-time, before Seymour kicked five goals to one to take a two-point lead at the main break.
The Lions extended their lead to eight points at three-quarter time.
Angus Murray, Nick Quigg, Oliver Munro and Tom Barnes kicked two each for the Lions.
Fletcher Paul (three goals) and Joshua Robertson (two) were Euroa's best in front of the sticks.
Shepparton United defeated Mooroopna by 31 points.
United led 26-7 at the first change, which proved the difference in the 11.12 (78) to 6.11 (47) win.
Kaedyn Napier (four goals), Jake Zerbato (two) and Jordan Wiggins (two) kicked multiple goals for United, while Liam Leahy kicked two goals for the Cats.
James Auld had a day out kicking eight goals in Shepparton Swans’ 30.18 (198) to 1.1 (7) victory against Tatura.
The Swans had 13 different goal-kickers in the 191-point win.
Jassiah Samkakai kicked Tatura's only goal in the final term.
Kyabram kept an inaccurate Shepparton outfit goalless in the opening half as it went on to win by 90 points.
The Bombers won 20.7 (127) to 4.13 (37).
Kyabram kicked 6.5 (41) to 0.8 (8) in the first half, before kicking eight goals to one in the third quarter.
Benalla and Mansfield's clash was abandoned early in the match after a Mansfield player was seriously injured. Both teams shared the points.
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