Southport have been relegated from the Blue Square Bet Premier after conceding two late goals away to Kettering.
Adam Cunnington gave the Poppies the lead when he converted from close range before Shaun Whalley volleyed in an equaliser from the edge of the area.
Kettering's Jean-Paul Marna missed a penalty but Southport failed to take advantage of the let-off.
Firstly Luke O'Neill struck a 20-yard free-kick before Jon Challinor drilled home in stoppage time.
Southport, who lost Aaron Turner and Kevin Lee to serious-looking knee injuries, almost made it 1-1 before the break when Karl Ledsham's header hit the crossbar.
But after Whalley had levelled the Sandgrounders' fate was sealed by O'Neill's strike just three minutes from time.
Southport are dropping back into the Blue Square Bet North after just one season in non-league football's top flight.
Kettering Town manager Marcus Law told BBC Radio Northampton:
"I'm all about winning football games and working extremely hard. You've seen that in our players today. We were going to show respect to everyone in that league.
"Sometimes it's not winning that golden trophy, it's just crossing the line. The challenges that were put in front of us this year, the fact that we're staying at Conference level by a good margin, that's fantastic.
"Wherever the lads next paths may lead, I'm very proud they played football for me."
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