Staring at a five-point deficit with time almost up and the ball at the back of the Tasman ruck, Otago looked down and out.
But it managed to get a free kick, put some phases together and sweep down to within a metre of the Tasman line.
Referee Keith Brown then awarded Otago a free kick past the 80min mark and No 8 Steven Setephano drove over to tie the scores.
Chris Noakes had the chance to win the game but his conversion from wide out flew across the posts.
Tasman started well on a sunny afternoon, then went to sleep and Otago took over, leading 16-8 at half-time.
Tasman came back into the game in the second half and all but closed the door, only for Otago to poke through at the end.
Otago's game was blighted by errors at critical times with a couple of big chances going to waste when passes were dropped.
Its passing was laboured at times but it was better at the breakdown and its line-out was first-class.
And to give it some credit, it showed some real character to come back into the game when all seemed lost.
First five-eighth Daniel Bowden had his best game in the Otago jersey, making line-breaks and showing some control.
A bump on the shoulder meant he could not take the final conversion, having not missed a kick all game.
Captain Craig Newby, freed from the openside flanking role for most of the day, had his best game of the year, and nabbed some crucial turnovers.
Winger Karne Hesketh scored a critical try in the first half - intercepting a pass and running 60m - when the visitors were struggling, and he ran hard all afternoon.
Otago had talked all week of wanting to make a good start but it lacked accuracy and in the first half spent only 1min inside the Tasman 22m line.
Tasman 21 (Robbie Malneck, Dan Hyatt tries; Miah Nikora 3 penalty goals, conversion), Otago 21 (Karne Hesketh, Steven Setephano tries; Daniel Bowden 3 penalty goals, conversion).
Half-time: Otago 16-8.
