Windsor & Eton manager Simon Lane was left stunned as he thought he had seen his side win their match in injury time only for a bizarre finale.
Jermaine McSporan gave the home side the lead early in the second half with Michael Chennels hitting two late strikes for Windsor before Ryan Curtin's late penalty.
Windsor had two early chances through Matt Seedel with the first being well saved by Simon Tricker and the second going just wide of the post.
Abingdon almost hit through Jermaine McSporan who got a shot off that looped up off Sam Mazurek and then headed against the bar by Anaclet Odihambo.
Ricci Dolan kept Tricker on his toes with a free kick that he whipped over the wall, heading for the top corner, which Tricker did well to get a hand on.
McSporan should have sent his side one up in first half injury time when Ryan Curtin set him up from a free kick and the shot was cleared off the line by Dave Tilbury.
McSporan continued to cause problems and within minutes of the re-start he managed to round Mazurek but his shot was cleared by Will Dunlop.
Abingdon managed to take the lead after 49 minutes when Windsor failed to clear a corner and Mazurek managed to scoop the ball off the line only for it to hit McSporan and go in.
Windsor pushed on to get back into the game and on 77 minutes got their reward when Abingdon's defence failed to clear a free kick allowing Jon Case to cross setting up Michael Chennels to head past Tricker.
Simon Lane thought his side had done enough to win the game when Chennels latched on to Tricker's fumble from Dunlop's shot to put the visitors ahead in injury time but their was a final twist in the tale.
After 5 minutes of injury time failure to clear a free kick saw a shot launched at the Windsor goal only for it to strike Tilbury's arm and a penalty awarded.
Ryan Curtin stepped up to take the penalty and duly put it past Mazurek.