Seymour put on a defensive masterclass at Kings Park, keeping Mansfield to just 13 goals, despite missing Meg Grbac and Alana Mascitti.
The Lions netted 34 goals of their own in the low-scoring affair, with Bec Beaton (19 goals) and Ellie O’Sullivan (15) leading the way.
Elle McDonald, Sarah Douglas and Rosie O’Sullivan also stood out for the home side in the big win.
For the Eagles, Jemma Blackall (eight goals) and Amy Dixon-Rielly (five) did all the scoring.
After building a solid lead of six goals at half-time, Seymour blew Mansfield out of the water in the second half, piling on 19 goals to four.
Lions playing-coach Laura Carland said she was glad her side grew in confidence after a ‘‘scrappy’’ first quarter.
‘‘Our last half was better with defensive pressure all down the court and precise feeds into the ring,’’ she said.
■Seymour’s B-grade side also enjoyed a big win, defeating Mansfield 48-27 after a huge second half saw them outscore the visitors by 15 goals.
Courtney Aldous and Georgia Engel were best on court, while Mariah Bauman (34 goals) and Lyndel O’Sullivan (14) were strong in attack.
Lions coach Marlee Koopman said she was rapt with the cohesion shown by her side.
‘‘It was probably one of our best games as a team,’’ she said.
‘‘The attacking end flowed effortlessly and our defenders worked hard to get the turnovers and bring the ball down the court.’’
The B-reserves, led by Sarah Waite, Isabella Morgan and Virginia Morgan, fought hard but went down 31-23 to Mansfield. Georgia Gregson scored 14 goals, while Annika Sutherland finished with six.
The under-17s enjoyed a seven-goal win against Mansfield with Rani Curry, Bianca Schache (26 goals) and Sophie Locke (28) best on court.
In the under-15s Ruby Martin netted a staggering 54 goals in her side’s 70-15 win against the visitors, with Abbey Cook, Madi Hager and Keely Wright best on court.