Two late goals sent Holbeach United into the preliminary round.
The Tigers knocked out Ely City on Saturday to set up a home tie against ON Chenecks in two weeks.
Substitute Charley Sanders broke the deadlock from the penalty spot with nine minutes left after George Zuerner had been fouled in the box.
Will Bird doubled the advantage on 87 minutes.
In a poor first-half display, the Tigers needed to show an improvement.
Alex Theobald fired wide for Ely who finally had the ball in the net midway through the second half.
A long ball was spilled by Rick Drury and prodded in by centre-back Tom Williams, but the referee ruled out the goal for a foul on the goalkeeper.
Just before half-time, Mitch Griffiths’ left-wing cross found Joe Smith but Harry Reynolds provided a great save.
As it looked likely to stay goalless, Zeurner was brought down and Sanders smashed the penalty straight down the middle.
Sanders topped off a great move by the Tigers to leave Bird with a tap-in.
Holbeach are without a midweek match, though, as the scheduled trip to Boston Town is off due to the Poachers’ FA Cup replay at Radford.
They face ON Chenecks at Carter’s Park on Saturday in the ChromaSport & Trophies United Counties League Premier Division.