Brighton thought they had rounded off an excellent week's work following their Wednesday night Carling Cup success on penalties against Manchester City when they led for the second time through Glenn Murray with the clock winding down.
But Northampton, whose gallant attempt to win at Premier League outfit Sunderland on Tuesday ended in penalty heartache, rescued a point in the fifth minute of stoppage time with Adebayo Akinfenwa's second of the afternoon when he headed in a corner from Danny Jackman.
Northampton dominated the first half and went closest when Colin Larkin's fierce shot was pushed away by Michels Kuipers.
But they fell behind three minutes before the break when Jason Crowe brought down Joe Anyinsah and Murray converted the spot-kick.
Kuipers did well to deny Karl Hawley in the 54th minute, while Brighton could have added to their lead when substitute Kevin Thornton curled in a 30-yard free kick which bounced on top of the crossbar.
Four minutes later it was 1-1 when Akinfenwa tussled for the ball in the box before poking a shot past Kuipers.
Liam Davis then had a blockbuster saved by the goalkeeper before the late drama, which began with Murray collecting a pass from Nicky Forster before drilling the ball past Fielding, only for Akinfenwa to square things up.