Danny Carey-Bertram thought he had fired Telford to the Trophy semis.
AFC Telford United were denied a definite place in the FA Trophy semi-finals by a last-gasp Southport goal.
Michael Powell's shot two minutes from time took a deflection past home keeper Ryan Young to level it up at 2-2.
Telford defender Gavin Cowan headed into his own net after just six minutes, but Jon Adams equalised almost immediately for the home side.
Danny Carey-Bertram pounced to make it 2-1 after his penalty was saved, and that looked to have won it for Telford.
"We're all disappointed, as we thought we'd done enough to win it," Telford boss Rob Smith told BBC Radio Shropshire.
"But we'll come out fighting for the second game. We've got nothing to fear there. Southport think it's all over, but it's not."
The replay is at Haig Avenue on Tuesday night (1945 GMT), forcing the cancellation of the already overworked Bucks' home league clash with Farsley Celtic.
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