Sean Roach at No 1 had a tight match with Sam Ma (Canterbury) but won the final hole to take the honours.
Team captain Andrew Hobbs was leading early but was one down with four to play.
However, Hobbs sank a 3m putt on the final green to clinch victory over Brent Ji.
Michael Minty, the Otago No 3, dominated Rodney Yee, winning by an impressive margin on the 13th green.
Philip Bungard was the only Otago player to lose in the morning.
Mark Brooks had his first win, beating seasoned Cantabrian Jason Sincock on the 16th green. In the afternoon Otago faced homeside Tasman and was looking to take the match but two one-down losses from No 1 and No 2 saw the encounter in a draw.
Tasman's Sean Riordan birdied 15, 16 and 17 to come from behind and beat Roach on the final green.
Hobbs was square playing the final hole but disaster struck and he lost one down to Sean Riordan's brother Blair.
The Otago tail wagged with Brooks trailing through five but winning three of the next four holes to be square at the turn.
Brooks made two amazing up-and-downs on the final holes to take the match with one hole to spare. Bungard was never behind and won the 17th hole to clinch the win.
Minty struggled early, turning three down and was four down with five holes to play.
He then made three birdies on the final five holes to escape with a valuable half to square the match.
Otago meets the strong Waikato quintet this morning.
Meanwhile, Bay of Plenty captain Mark Smith celebrated his 50th appearance for the province as his team marched on in defence of its title.
Bay of Plenty was pushed by Southland before winning 4-1 to remain one of three unbeaten teams after two days of competition at Greenacres Golf Club.
With the bye already under its belt, Bay of Plenty shares the lead with three wins in section two along with 2005 champion North Harbour, with Hawkes Bay next on two wins and a half.
It is a dog fight in the other section where all teams have been beaten.
Otago clings to the lead with two wins and a half, with Manawatu-Wanganui, Wellington and Waikato all with two wins.
Wellington bounced back after its loss on Tuesday with two wins to be in third place ahead of Waikato and host Tasman.
Canterbury and Auckland will need a miracle if they are to remain after post-section play.
Bay of Plenty accounted for Aorangi-South Canterbury and Southland yesterday, both by 4-1 margins.
North Harbour had two impressive victories, dropping just one game and a-half in wins over Taranaki and Poverty Bay-East Coast.
Hawkes Bay posted a 5-0 whitewash of Poverty Bay-East Coast before finding winless Northland a major obstacle in the afternoon to square the contest 2 each.
Manawatu-Wanganui bounced back from a 2-3 loss to Tasman with a 4-1 win over Waikato yesterday afternoon.
Wellington recovered from a loss on Tuesday to beat rival Auckland before dispatching Canterbury 4-1.
There is one round today with the final two rounds tomorrow ahead of the semifinals and final on Saturday.
