Two of the wins were secured only in third-set tiebreaks and after being within two points of losing in the top single, which featured Mitchell Sizemore, who reversed his Otago Open semifinal loss to titleholder Charlie Tomlinson.
Tomlinson took the first set 6-4 but Sizemore relaxed and went on a nine-game run to lead 3-0 in the third set, only for Tomlinson to get four games in a row himself.
At 5-5, Sizemore broke serve but then threw in two double faults when serving for the match. In the deciding tiebreak, he led 4-0 but was caught again at 5-5. At match point, he sent a return just long but then hit a very close winner and a big serve to close it out.
The doubles followed a similar pattern. Taieri won the first set 7-6, lost the second to love but St Clair clinched the match tiebreak. It was an easy winner in the other rubbers.
Balmacewen leads John McGlashan 4-0 from play on Saturday with two rubbers to complete. If it wins both, St Clair could only hope to share the title.
The deciding factor will be No1 Paddy Ou, who can clinch the shield for Balmacewen if he can beat either Carlos Reid or Sizemore in the unplayed rubbers.
St Clair would also have to win its remaining matches in its incomplete tie with the leader.
In the other tie, OBHS edged Eastern Harbour in a marathon that went to sets countback 9-8 after rubbers were even at 3-3.
In the top single, former Otago rep and doubles titleholder Phil Mirfin outlasted joint most improved winner Thomas Chiang after falling behind a set, then winning 6-3, 6-2 as his schoolboy opponent showed increasing frustration.
