The visitors led 8-7 at halftime thanks to a try from Wakatipu loosie Henry Youngman and a Rhys Harrold penalty, but could not score again.
Conditions were tough but Otago Country coach Roger Cotton said some of his side's execution was poor.
''We actually made a few mistakes and they capitalised on that.''
''We didn't exit from our 22m and they came up with points. I think we need to be more accurate and some players need to understand what their roles are.''
Cotton said Otago Country found some continuity, especially in the first half, and the defence was ''very good''.
He was not too worried about the loss, pointing out it was the opening game and the side's structures were still being put in place.
Tight forwards Tim O'Neill, Kerrod Baldwin and Blair van der Voort had strong outings and Cotton was pleased with the set piece.
Matakanui centre Scott Milne was Otago Country's best on the day.
Southland Country scored tries either side of halftime, one to Michael McKee and the other to Jackson Wallace. Waikaka's Wallace also kicked a penalty in the second as well as converting both tries.
Otago Country's next game is against Southland B in Te Anau next weekend.
Otago B beat South Canterbury 10-7 in a warm up game in Dunedin on Saturday.
All 26 Otago B players, along with ITM Cup hooker Sam Anderson Heather, had a run in the fairly scrappy encounter.
South Canterbury led 7-3 at halftime before Dillon Hunt scored a try for Otago B.
Country rugby
The scores
Southland Country 17
Michael McKee, Jackson Wallace tries; Wallace 2 con, pen
Otago Country 8
Henry Youngman try; Rhys Harrold pen
Halftime: Otago Country 8-7.
