Despite losing the top two games, St Clair emerged with a comfortable win as the St Clair tail wagged with four good wins.
Duncan Croudis continued his unbeaten run, finishing 4-under-par to beat Brent McEwan 4 and 3.
Croudis, home on holiday from his golf scholarship at Iowa University, had his fourth convincing win since returning home.
He was 2-up at the turn which was reduced to one when McEwan birdied the 10th hole but Croudis closed the match out, winning the 12th with a par and the 14th and 15th with birdies.
Unfortunately, Otago will be without his services in the interprovincial tournament at Balmacewen later this year as it clashes with his university examinations.
Otago B captain Michael Smith edged ahead of Tony Giles in a tight contest after turning 1-up.
Smith won the 14th to go two ahead and took the match when the pair halved the next four holes.
St Clair No 3 Stephen Hitchcox continued his fine matchplay season, leading Tony Ruddenklau by three at the turn.
Hitchcox birdied the final two holes to take the match with three holes to spare.
Clayton More, the St Clair No 4, won the first two holes and turned 3-up but lost the 10th to reduce his lead to two.
But he beat Otago's Mark Paterson on three holes early on the homeward nine to win 5 and 4.
The match between Greg Johnson and Daniel Elder was no race when St Clair's Johnson won five of the first seven holes.
Elder fought back to turn 3-down, but it was too little, too late, as Johnson won with three holes to spare.
St Clair greenkeeper Andrew Hobbs was always going to be hard to beat playing at No 5 and put up an expected solid performance.
Jason Hughes, sporting a black eye from his celebrity boxing defeat one week ago, kept within touch with his putter working well, but Hobbs gave St Clair its fourth win finishing the match on the 16th green.
