The team is five points ahead of Chisholm Park and North Otago, which both have four points after a win and a draw in the last three rounds.
The top St Clair golfers were in top form with Brent McEwan, Stephen Hitchcox, Andrew Hobbs and veteran Kim McDonald all carding rounds of 3-under par to win their matches in a canter against their Oamaru opponents.
Kris Rush was the only North Otago golfer to prosper when he beat Jason Pegler in a close contest which finished on the final green.
The nightmare continues for defending champion Otago, which posted its third consecutive 3-3 draw in this year's series.
With one point for a draw and three for a win, Otago is six points off the pace and will need to blitz St Clair when they meet on the Corstorphine course in two weeks' time, to have any chance of retaining the title.
For Chisholm Park, Antony McCullough, Sean Geary and Peter Rae posted 4 and 3 wins against their Otago counterparts who failed to capitalise on playing at home.
Brandon Hodgson (No 2) and Thomas Facer (No 4) both posted wins for Otago and the Park team looked set to take the honours.
But Balmacewen's No 1, Tyrone Ratahi, sank a four-metre putt on the final green to edge ahead of Kyle Geary and secure the draw.
