A controversial penalty gave the Middlesex side an unlikely Buckingham Road replay after The Ducks had looked set for an easy win over the Vauxhall Opel League minnows at Preston Park.
Things started to according to plan for the visitors when Cliff Hercules' 10th goal of the season gave them the lead on 15 minutes with a looping header from Derek Duggan's free kick.
It was 2-0 on 27 when Hercules flicked on Dave Botterill's long throw at the near post and Duggan buried his volley past Mick Kavanagh.
Ducks keeper Jason Edworthy (in for the unavailable Keith Baker) pulled off a great save with his legs to deny Theo Edgar on 58 but a minute later, the hosts pulled one back when Tony Kelly headed in Gary Manning's free kick.
Harefield's Gary Downes was sent off on 60 for elbowing Duggan in the face before the hosts levelled on 67 when Edworthy was adjudged by the referee to have mpeded Edgar and Steve Walker blasted home from the penalty spot.
