With 4.5 wins and 20 games from five outings, St Clair is two points ahead of Otago B and Otago A with 15 and 14.5 games respectively.
Otago B had started the day in second place but, for the second time, Otago A beat Otago B 3.5-2.5 at Balmacewen.
The Balmacewen teams are neck and neck, and the B team holds a half-game advantage after showing better form when playing away from home.
Tyrone Ratahi was 2-under-par beating Michael Smith 3 and 2 in the battle of the No 1 players but Duncan Croudis evened the score for the Bs at No 2.
Croudis is home for a break from his scholarship at Iowa University and showed good form at two under beating Cameron Grant by 5 and 3.
Murray Edgar, the Otago A No 3 and captain, gave Brandon Hodgson little chance with a putting blitz that saw him need only 19 putts in the 15 holes required to finish the match.
Luke Murdoch posted a win for the A team while Tony Ruddenklau (Otago B) beat Gus Rattray with one hole to spare.
The outcome depended on the match between Thomas Gillan (Otago A) and Mark Patterson and the pair were square with two holes to play.
Gillan made a crucial par to win the 16th and go one ahead and the result became certain when the pair halved the 17th.
At St Clair, Brent McEwan continued his winning form at No 1, this time at the expense of Kyle Geary, by 4 and 3.
Mark Collie (Chisholm Park) headed Tony Giles at dormie two up but Giles kept the match alive birdieing the 17th, only to lose on the final green.
Stephen Hitchcox and Greg Johnson had decisive wins for St Clair while No 6 Paul Brouwer posted the biggest winning margin, beating Conor Jamison within 13 holes.
Cody McMullan secured the other win for the Park team beating Clayton More by 2 and 1.
