The Mariners won their first match of the double header before falling to Claremont-Nedlands, who swept the southwest metropolitan group aside to gain passage to the next round.
Fremantle were no match for the Mariners, despite playing on their home ground at Stevens Reserve.
They made 9-114 as the bowlers shared the spoils while keeping the batsmen in check.
The visitors romped to the total with eight wickets and 37 balls to spare, as Brayden Sutton slammed six fours and two sixes in 54 off 34 deliveries.
Craig Simmons and Brendon Diamanti struck 47 and 45 respectively to anchor different halves of Rockingham-Mandurah’s innings against Claremont-Nedlands.
But no one else came to the party and they were dismissed for 136.
The Tigers used up all but five balls of their dig to make it to 3-137 and went through as one of six district clubs into the last 12 of the T20 league.
No play was possible at Lark Hill on Saturday, meaning the firsts, thirds and under-17s will need to pull a rabbit out of their hats to force a result in just one day.
Rockingham-Mandurah had the better of University in the play that was possible on Saturday.
At James Oval, the second grade side dismissed the students for 140 to put themselves in the box seat.
Jamie Ryan (3-48) and state under 17 squad member Kyle Gardiner (3-31) kept striking in the team’s best day of the season as they searched for their first win.
The Mariners safely made it to stumps at 0-7.
Youngster Lachlan Pratt struck a important century to give the fourths an opportunity before a clever declaration yielded a University wicket before the close of play.
Pratt scored a half-century in round three against Gosnells, but the under-17s batsman learnt from that and doubled its value as the Mariners declared at 8-204 at UWA Sports Park.
Guy Lewis took the wicket to leave the home team at 1-22.
Caitlin Crocetta gained plenty of experience after a tough time with the Under 15s West Australians in the Female National Championships in New South Wales. The team has yet to taste success, but Crocetta has played in all six matches.
Next week the under 13 and 14s sides play Fremantle at Lark Hill on Sunday in round four.