Mannum and Monarto will play off in the Murray Towns Cricket Association's A grade grand final at Johnstone Park on Saturday after winning their respective semis.
In the B grade, Monarto defeated the Ngarrindjeri Swans by 54 runs and will play Karoonda, who upset top side Mypolonga by 73 runs.
Kym Edwards and Simon Williams made half-tons for Monarto this week, while Jake Venning and Daniel Rankine each took four wickets for Karoonda.
The C grade's grand finalists will be Claypans, who restricted Mypolonga's scoring to win by 58 runs, and Monarto, who passed Meningie's total with one wicket down and more than half an innings to spare.
Half-centuries were scored by Claypans' Paul Donald and Monarto's Ian Bates.
Mypolonga v Monarto
The Black Caps' A graders earned the right to face a side that has been on top of the ladder since October by squeaking past Mypolonga with four balls to spare.
The scorecard recorded the margin as being two wickets, but the match could have gone either way.
The visitors lost 5/15 in the later stages of their innings, including two run-outs; then a third run-out sent Harry Miles back to the shed when Monarto were one run shy of equallying Mypo's score.
But Brad Lienert (5 off 3) and Jarrad Kowald (4 off 1) survived and saw off the threat.
Earlier, Mypolonga had put 158 on the board before being bowled out.
Dependable Jared Marston scored a steady 43 and Aaron Zrim (27) and Trent Sherman (25) also chipped in, but wickets fell regularly after Marston was bowled by Ty Pfeiffer.
Michael Elliott took 3/27 for the Black Caps and Miles had a couple of catches.
In Monarto's innings, Pfeiffer (47), Jacob Rance (39) and Harrison Webb (26) were the main contributors, but like their opponents, their lower order batsmen struggled to score or stick around.
Sherman took 3/31 for Mypo before the Tigers' season ended in heartbreaking fashion, while Zrim bowled 10 overs for just 12 runs and threw down Webb's stumps.
Mannum v Wanderers
At Mannum Oval, the home side defeated Wanderers by five wickets with almost 19 overs to spare.
The visitors nearly batted out their overs, but were eventually dismissed for a below-par 111 with eight balls left.
Matthew Thompson recorded the savage figures of 3/16 off 10 overs, including five maidens, while Nick Lindner took three catches.
The run chase was not a cake walk, as the first wicket fell when the score was just three.
But Thompson (31*) stuck around in the middle until his side got the win, after Justin Maloney (27) and Jayden Krollig (21) laid much of the ground work.
Wanderers had not uploaded their scorecard to My Cricket at the time of publication.