The St Clair golfers suffered their first loss in the series, going down by 2.5 to 3.5 to North Otago in Oamaru.
At Chisholm Park, the local team was always going to test the Balmacewen golfers who are now reeling at the margin, with Park golfers winning five of the six matches.
Despite the loss, St Clair is two points ahead of the pack, with Chisholm Park and the two Otago teams tied on 2.5 points.
The large winning margin has hoisted Chisholm Park into second place ahead of the Balmacewen teams with a superior game tally.
The upsets have created a log jam with Noth Otago only half a point behind the pack, setting up an exciting final three rounds.
The match at North Otago was a tight tussle, with five matches finishing on the final green, while St Clair No 1 Brent McEwan beat Michael Ormandy one hole earlier.
North Otago's success came down to a sterling performance by the club's two juniors, with Kris Rush and Cameron Ryder beating two experienced St Clair golfers.
Rush beat Andrew Hobbs while Ryder accounted for Greg Johnson. Both matches finished on the final green.
At No 6, Gary Watling gave the home team its third win and it was 3 to 2 when Michael Minty (St Clair) joined McEwan in the winner's circle.
North Otago greenkeeper Gary Creedy gave his team the edge when he halved with St Clair No 2 Stephen Hitchcox.
At Chisholm Park, the middle order of Lyndon Chalmers and Sean Geary set the scene by winning early in 15 holes.
Park No 6 Peter Rae beat Craig Lyall to give Park three wins while, after a double-bogey on the first hole, Luke Murdoch (Otago No 5) finished two-under to beat Mathew Heaton by 8 and 7.
The Otago top pair then had to win to salvage a half but both John McIntee and Daniel Barnett trailed with three holes to play.
The Park's leading pair of Kyle Geary and Mark Collie both notched wins to beat Otago A by an embarrassing margin.
Long-time pennants golfer Sean Geary summed up the day when he admitted his Park team had never before won by this margin.
