After finishing top of the league and only losing twice during the regular season and finals, Mandurah would have fancied its chances against the Seals, who had to travel despite earning the right to host the game.
Shoalwater won the toss, elected to bat on a beautiful Mandurah day and made a solid start.
The Seals reached 30 before losing Brandon Burt (24), Hammad Khan (1) and Nick Milligan (2) in quick succession to be 3-31.
Mandurah was making inroads but Shoalwater skipper Dudley Cortland and Stuart Heazlewood steadied the ship before Heazlewood departed for 21.
Cortland (1`4) followed shortly after, as did Graham Spinks and Daniel Abel, who both failed to trouble the scorers.
Precariously placed at 7-91, Mandurah would have been confident of wrapping up the Seals’ innings quickly but Mitchell Smith (89no) and Brendan Gillian (47) combined to rescue their side, guiding Shoalwater to a competitive 8-207.
Paul Okey claimed 3-45 off 10 overs to be Mandurah’s best with the ball.
Mandurah needed a good start but its didn’t come with Paul Okey (0) out lbw with the score at just 1. Ben Drummond (3) followed shortly after, leaving Mandurah at 2-4.
Skipper Jeremy Leatherbarrow (14) was caught off the bowling of Seth Kennedy (3-27) to leave his side at 3-18.
Justin Solly played the lone hand for Mandurah, making a fine 70 while Rhys Donald (26) supported ably. Donald departed with the score at 69 before David Virgo (0) and Reece Powell (4) departed in quick succession, leaving Mandurah in a similar position to Shoalwater at 6-83.
Ian Lattimore (39) combined with Solly for a 75 run partnership, reaching 158 before the former departed.
Another stream of wickets followed with David Schonberger (1) and Solly falling, leaving Mandurah hopelessly marooned at 9-164. Gehan Fernando (2) was the last wicket to fall, caught and bowled Grant Coles to enable Shoalwater to claim its second A grade flag.
Both Mandurah and Shoalwater will compete in the Peel Premier League T20 finals series this weekend at Pinjarra Turf.