Otago will meet the favoured Wellington team on its home Paraparaumu course.
Auckland was unbeaten and a clear winner of division one, with Otago and Taranaki scoring 3.5 points each but Otago going through on a superior game tally.
The other semifinalists, Auckland, Wellington and North Harbour, have won the title 25 times among them.
Thirteen of the 15 provincial teams were still in with a chance of qualifying for the semifinals at the start of yesterday's final two rounds of section play.
This is the first time Otago has made it this far since manager Ben Gallie played in the team in 2001.
Otago looked good against Bay of Plenty in the morning and after seven holes Brent McEwan and Duncan Croudis were 3-up while No 5 Simon Hollyer led by two.
But the team lost the momentum in the middle six holes and was unable to recover. Croudis was the sole winner, 3 and 2 over Landyn Edwards.
In the afternoon Hollyer was promoted to No 4 with reserve Tyrone Ratahi making his debut at No 5 at the expense of Hamish Ireland.
It was crucial for Otago to win, and win well. McEwan continued to play outstanding golf going out in 5-under 31 with a "ginger run" of birdies on 5, 6, 7 and 8.
He finished with a 68 for a 5 and 4 win while Croudis was also playing exceptional golf. He turned two behind but rallied on the back nine for a 2 and 1 victory.
That win means that as reserve in 2008, a late arrival from China in 2009 and with six wins this year, the 19-year-old is unbeaten in 11 matches at the interprovincial tournament.
At No 3 Michael Smith trailed early but dug deep to be 1-up playing the last only to face a birdie 4 from his opponent and halve the game.
Hollyer had an up and down match but made a birdie 4 on the final hole to secure a half.
A nervous Ratahi got behind early and, despite being two down at the turn, won 10, 11, 13 and 15 to reverse the score.
Unfortunately he lost the next two holes to be square playing the final hole.
Manager Gallie was rapt when the youngster holed a 3m putt for a birdie 4 to secure the win.
"We knew we had Brent in at this stage and getting the second win took the pressure off our middle order and put it firmly back on the Man-wangs," Gallie said.
Auckland won its spot at the top of division one with a squeaky 3-2 win over Waikato yesterday morning on the back of a brilliant eagle on the final hole for a 1-up win by Eisenhower representative Ryan Fox.
It could afford the luxury of a final-round loss to Bay of Plenty but will be more serious today as it chases its first title in 15 years.
In division two, North Harbour scored two whitewash wins over winless Poverty Bay East Coast and Aorangi.
Wellington dug deep yesterday morning to edge out Southland 3-2 with No 5 James Betts, with only one win to his credit before yesterday, grabbing the crucial 1-up victory.
It then faced a knockout encounter against Canterbury, which was in contention following a morning win over Hawkes Bay.
It proved one-way traffic for the host with a 5-0 win and the opportunity to win a 13th interprovincial title today.
- Additional reporting by NZPA
