Biggleswade have come through five matches for the chance to take on York, whose FA Cup pedigree includes a run all the way to the semi-finals in 1955.
Incredibly, eighth-tier Biggleswade saw off Canvey Island 1-0 in the previous round despite finishing the game with only nine men on the pitch after Michael Fisher and Charlie Hayford had been sent off.
“I got through it by praying,” said Northfield.
“For 20 minutes we weren’t very good, we struggled to get a foothold, and weirdly enough, the sending-off (of Fisher) got us playing how I wanted us to play.
“We stayed positive, got on the front foot, created one or two openings and then scored our goal from a great header from Lawrie Marsh late in the half.
“Second half, I felt we were matching a lot of what they did although obviously we had to defend an awful lot of balls into our box. You just block up holes, block up the angles and keep it in front of you.
“George Rose in goal made two or three unreal saves, one with his feet. Charlie Hayford, the second player to be sent off, cleared one off the line. Last five minutes we went to a 4-4-0 and it’s just a big rearguard action.”
Fisher will miss the game against York after his red-card appeal was turned down, but Hayford can play as he only received a one-match ban for two yellows against Canvey Island.