The first three grades, as well as the Under-15s and Under-17s are well on top and will look to press home that advantage this Saturday before a massive one-day semi-final on Sunday at 10.30am, with the Past Players function also taking place at Lark Hill.
In first grade, South Perth won the toss and batted but Leon Coombs (2-29) set them back with two quick wickets.
The visitors constructed a 47 and then an 85-run partnership to get to 4-146.
Once the Mariners forced open the door at Lark Hill, they smashed it down as all the bowlers brought their sledgehammers.
Lachlan Pratt picked up key wickets throughout to end with 4-40, the best haul of his young seven game career.
Craig Simmons (2-41), Joel Marion (1-32) and Kyle Gardiner (1-32) added to the effort to keep South Perth to 205.
Mitch Green (26 n.o.) and Dane Ugle (14n.o.) will resume on Saturday with Rockingham-Mandurah at 1-48 in what could prove to be a big weekend for the club.
The following day, the Mariners will host Subiaco-Floreat for the right to make their first-ever appearance in a 50-over final.
Vince Poller and Liam Mead spearheaded a massive batting feast for second grade at Richardson Park.
Poller fell for 97 but he and number three Mead piled on the runs in the first two sessions to open it up for quick runs at the end.
Mead struck 81 as 10 of the batsmen got to double figures with Rockingham-Mandurah finishing on an imposing 9-361.
Third grade will need another 117 runs after the bowlers dismissed South Perth for 162.
Wesley Steele (3-33) and Jordan Brokate (3-36) were the chief destroyers and gave the Mariners 19 overs to get after the total. Carey Green (30 n.o.) and Craig Anderson (10 n.o.) shepherded the team to 1-46 by stumps.
Ronan Hogarth was the bright spot on day one for fourth grade as South Perth are just 42 runs behind at stumps.
The Under-15s batsman made 58 out of his team’s total of 137 in just his second senior match.
South Perth are 1-95 as captain Lewis Pitts swung the changes with nine bowlers used in the 32 overs.
Joel Humble blasted 144 in the Under-17s’ mammoth score of 5-302 at Lark Hill.
The number four’s innings consisted of 20 boundaries and two sixes from 140 deliveries as other contributions from Jaxon Standing (34), Wesley Steele (31) and Barend Grove (25) boosted the tally.
Kai Harrison’s 4-16 helped skittle South Perth’s Under-15s for 134 at Richardson Park. The opener struck three times early and wrapped up the innings from 10.1 overs.
The Mariners shot out to 0-36 from eight overs by the close of play.
Caitlin Crocetta made 48 in a nine-wicket loss to Midland-Guildford women’s Under-18s as the Swans overhauled Rockingham-Mandurah’s 77 despite Crocetta’s 33-ball gem.
The Under-15 girls were outplayed by Melville in a 64-run loss.
The Under-14s boys won by 14 runs against South Perth in a closely-fought match throughout but the Under-13s made a good fist of chasing down South Perth’s 4-211 to end on 4-155 in the 40 over fixture.