Winning the toss and electing to bat, Yea posted 170 from 44.1 overs.
Marc Steiner produced the standout innings of 47 from just 39 deliveries, including six fours and two sixes, after Yea had been reduced to 5-66.
Jack Christie contributed 21, while Jake Fish (16), Tyler Reed (15) and captain Thomas White (14) also made useful contributions.
Seymour's bowlers shared the wickets, with Cameron Evans particularly impressive, claiming 2-16 from nine overs, including three maidens.
Brodey Pointon (2-46) and Simon Van Duinen (2-12) also claimed two wickets apiece, while Dan Bergowicz, Lachlan Drummond, Hugh Smith and Braidon Horkings each picked up one.
Chasing 171 for victory, Seymour struggled early, slipping to 4-58 as Yea's bowlers made regular breakthroughs.
Drummond then produced a counter-attacking innings of 75 from 67 deliveries, including nine fours and two sixes, to keep the home side in the contest.
His dismissal at 7-147 proved decisive, with 24 runs still required. Seymour’s lower order battled on but the side was dismissed for 161 in the 40th over.
Yea’s bowling attack produced a strong collective performance, with Reed (2-26), Steiner (2-27), Cameron Armstrong (2-13) and Andrew Butterworth (2-10) each claiming two wickets.
Wicket-keeper Beau Hawkins completed three catches behind the stumps, while Steiner added two catches to his contributions with bat and ball.
