Stoppage-time goals from Chris Lever and Jonathan Brown ensured Southport came back from a goal behind to beat 10-man Mansfield.
John Dempster put the Stags ahead with a six-yard strike before Lever fired in from Alan Moogan's free-kick to level.
The visitors were reduced to 10 men after Ritchie Sutton received a second yellow card.
Lever then scored a penalty, after Marcus Kelly fouled Shaun Whalley, before Brown fired from close range.
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Mansfield manager Paul Cox told BBC Radio Nottingham:
"I thought the performance was excellent but I am just disappointed in the result.
"Even with 10 men we did really well and created chances, but we felt the sucker-punch in the 90th minute.
"If we produce similar performances, then results will come our way."