The Stags were edged 25-17 by Counties Manukau in Pukekohe last night.
The visiting side needed to win to keep its Championship semifinal prospects alive.
It was chasing its first away Mitre 10 Cup victory in five years and got into a position to win.
But the game slipped away when Counties first five-eighth Jason Robertson drilled a penalty with eight minutes remaining.
That stretched the margin to eight points which proved out of reach.
Both teams scored late tries but it did not threaten to change the result.
The Stags will be able to reflect on a much improved effort, though.
The team has struggled in recent seasons but managed three wins this year — the first time it has achieved that many since 2014.
A bitterly disappointed captain Tony Lamborn finished the campaign the way he started. He put everything into the match and was outstanding once again.
"I wouldn’t say I’m disappointed in the season," Lamborn told the Sky commentary team.
"We ticked a lot of boxes ... but I would have liked to have made a semi and win this game. But, hey, that is just fate, I guess."
Lamborn was well supported by his pack which had the better of the scrums.
The defence was solid again but the Stags failed to convert their attacking opportunities which was a problem all season long.
The opening 15 minutes was played almost exclusively in Southland’s half. Lock Mike McKee provided some relief when he snatched an intercept and ran the best part of 40m.
A few minutes later, fullback Rory van Vugt sold a dummy and slipped through a gap.
But the ball was lost in a maul and Counties was able to swing back on to attack, thanks in part to a great carry by powerful No8 Viliami Taulani from the base of a scrum.
Southland lost hooker Greg Pleasants-Tate to a sternum complaint with 12 minutes remaining in the first spell. Shortly after he departed, Counties finally breached Southland’s stout defence.
Centre Sione Molia went over in the corner. But loose forward Charles Alaimalo never gave up and dragged one of his boots into touch around about the same time as he grounded the ball.
It was a photo finish but the try was awarded.
Alaimalo was nearly a hero but made a quick transition into villain when he was yellow-carded for not retreated 10m and tackling nippy halfback Cameron Roigard before the break.
Roigard helped double the lead shortly half the resumption. He darted over from the back of a rolling maul.
Southland hit back almost immediately. Winger Tevita Latu got himself involved close to the ruck and crashed over.
The try went unconverted but the visiting team had got itself back into the contest.
Lamborn took a break from tackling to shunt his way over from another dominant scrum.
Scott Eade landed the extras to trim the lead to 14-12 with 20 minutes and small change remaining.
But Robertson extended the margin with a couple of penalties and victory drifted away.
