Otago beat Aorangi by a convincing 9 to 1 game margin but was tested by Southland after the teams tied 2.5 each overnight.
A strong finish yesterday helped Otago to a 5.5 to 4.5 win, with a two-game winning margin for the top five players.
Otago's success continued in the under-21 contest, where the Otago players dominated a 10.5 to 1.5 game tally.
This six-strong team included Harry Smith, Connor Ross and Jakob Bleach, who competed in the junior interprovincial in Cambridge last week and continued their good form in Invercargill.
But the Southland masters (over-40) team beat Otago in the two-round match played on the Cromwell course.
For Otago, Simon Boland (Queenstown) was the only unbeaten player, beating Gary Radka by an impressive 8 and 7 on Saturday and halving with Craig O'Rorke yesterday.
In the men's team, No1 Brent McEwan was unbeaten with a win and a half, while No3 Duncan Croudis had two wins.
The Otago tail wagged and Sungwoo Han, Ryan Bellamy and Daniel Elder all posted two wins.
No4 Inia Logan made an impressive start to his Saturday round, after losing the first hole to a birdie 3.
He retaliated with eagle, birdie, birdie and birdie to be five under par after the first five holes, eventually beating Aorangi's Daniel Perham.
With players fighting for places in the eight-man team for the South Island at Westport, Nick Borren, Logan, Brandon Hodgson, Fraser MacLachlan and Chris Snow all had one win each.
American world No 1 Jordan Spieth has been named the PGA Tour's Player of the Year after a stellar 2014-15 campaign highlighted by two major victories among his five wins, Reuters reports.
The 22-year-old landed the honour after clinching the first two majors of the season - the Masters and US Open - before finishing one shot out of a British Open playoff in July and being runner-up at the PGA Championship in August.
