League leaders London Colney claimed a 3-1 win at Leighton Town to move 12 points clear at the top of the South Midlands Premier Division.
Spencer Clarke-Mardel put the ball in the net early on but his effort was ruled out for offside.
The opening goal came for the Blueboys when Dave Parkinson set up Jack Woods for his finish.
But their lead was cancelled out midway through the half when goalkeeper Tom Gowans missed the ball and Martin Griggs headed home.
The visitors restored their lead just before the break when Parkinson beat a defender and fired a 16-yard strike into the net.
Griggs almost levelled the game in the second half but he was denied by Gowans.
It was a crucial moment as London Colney extended their lead midway through the half. Clarke-Mardel won the ball and from the tightest of angles unleashed a low strike past goalkeeper Jack Sillitoe.
The Blueboys visit Wembley on Saturday.