Otago A had won the previous two matches 3.5-2.5 but the B team has been strengthened by the acquisition of Duncan Croudis who having a break from his University college studies.
Croudis played at No 1 and posted a 4 and 2 win over Tyrone Ratahi, while Michael Smith beat Otago A No 2 Luke Murdoch 3 and 1.
Otago B's next three players were Tony Ruddenklau, Mark Paterson and Daniel Elder who all finished their matches with two holes to spare.
Otago A's only win came from Thomas Gillan, who was always in control, beating Gregor Croudis 8 and 7.
The match was played in marginal conditions, with some flooding on the greens.
The margin looked set to be closer when Ruddenklau and his opponent Murray Edgar were tied after 13 holes.
But Ruddenklau parred the 14th and 15th before birdieing the 16th to snatch the win.
St Clair hosts Otago B in the final next Saturday. After leading during the home-and-away round robin series, St Clair has a home final.
St Clair has a very experienced line-up and Otago B will have to play well to win.
• Phil Mickelson and defending champion Luke Donald profited from a glut of birdies in the third round of the Scottish Open yesterday to tuck in behind leader Francesco Molinari, Reuters reports.
Mickelson's 7-under 65 included six birdies on the closing nine as the four-time major winner closed to within three shots of Molinari (67) whose 54-hole 17-under total of 199 put him a stroke ahead of Anders Hansen (65).
World No 1 Donald, tied for ninth with six others, mixed seven birdies with three bogies for a 68, a shot behind Mickelson, home favourites Martin Laird (64) and Peter Whiteford (66), and Swede Alexander Noren (70).
