Before this year's series reached the halfway stage, St Clair had opened up a four-point lead and looked to run away with the event.
But Otago's win brings the team to within two points of the defending champion and keeps the interest high during the second half of the series.
Only St Clair and Otago have played five games.
Bad weather has left Taieri and Chisholm Park with a game in hand while North Otago and South Otago have two games to play.
The match between the leaders looked like being a tie when Paul Brouwer holed a 6m putt on the final green but Otago's Murray Edgar was equal to the task, holing a 1.5m putt to secure the win.
Winter golf conditions made low scoring difficult but all of the Otago golfers were close to par.
St Clair No 1 Brent McEwan played some immaculate golf from tee to green, only missing one green in regulation.
However, he had 37 putts which kept Otago's Michael Smith in the match until the 17th green.
St Clair dominated the top five matches with three wins and a half but the Otago tail wagged with Murray Edgar, Tyrone Ratahi and Luke Geddes all posting wins by narrow margins.
