For the second week in a row, Brent McEwan was the difference which tipped the honours in favour of the Corstorphine golfers.
A shrewd move to drop the St Clair No 1 down to No. 3 for the decider paid dividends, as his 3 and 2 win over Tyrone Ratahi was the difference in the countback, as all of the other games finished on the final green.
McEwan's input was not restricted to his own match as, when No. 2 Stephen Hitchcox replaced his marked ball in an incorrect position, he reminded Hitchcox to replace his marker in the correct position.
Failure to do so would have led to a loss of hole and an Otago Blue win.
Having dominated the series with seven wins and two halves an unbeaten Otago Blue team was devastated at the final result, which once again made it the bridesmaid of the 12-week competition.
At No 6, Luke Murdoch made six birdies in the first eight holes but was still only three ahead of St Clair green keeper Andrew Hobbs.
But Hobbs retaliated with a string of birdies on the homeward nine and, despite three putting the final green, finished tied with Murdoch.
Jamie Anstiss, the Otago No 5, sank a crucial 2m downhill putt on the final green to beat St Clair veteran Tony Giles.
But St Clair's middle order rallied when Chris Snow beat Jason Hughes by two and McEwan beat Ratahi.
Otago No 1 Brandon Hodgson was three up on Clayton More but More won 14, 15 and 16 to get back to square.
Hodgson put the result beyond doubt when he all but holed out with a massive tee-shot on the par 4 17th.
Hodgson then won the final hole for a two-up win and the outcome was left with Otago Blue No 2 Michael Smith.
He was one up playing the final hole but his approach finished in the right-hand bunker and he failed to halve the hole with Hitchcox.
St Clair will now go forward to the provincial final against the top teams from Central, North and South Otago.
