Goals at the end of each half sent Holbeach United into the Knockout Cup final for the first time since 1990.
Josh Ford – who scored 21 goals for Wisbech Town last season – converted a penalty against his former club two minutes before the break.
Teenage substitute Sean Coughlan’s superb effort on 87 minutes sealed victory for the Tigers.
They meet Peterborough Sports in the final to be played on Bank Holiday Monday, May 2 (3pm kick-off) at the Haydon Whitham Stadium, home of Deeping Rangers.
The semi-final at Carter’s Park on Wednesday night proved to be a tense affair as the teams cancelled each other out for long periods.
However, Holbeach took control as Ford was tripped in the box by Luke Wilson and the striker smashed his spot-kick into the roof of the net.
Just moments later, Rick Drury pushed out a drive from Luke Hipwell but the Tigers’ number one was generally untroubled with plenty of protection in front of him.
Ford was denied by a last-gasp block from Wilson and Jordan Thomas’ effort was hooked off the line by the Wisbech defender.
Matthew Sparrow’s volley went into the side netting and another attempt was too high before Drury held onto Adam Millson’s header.
Coughlan came off the bench to show raw pace and sheer determination which can terrify defences.
So it proved again as he battled for a bouncing ball around the edge of the area and produced a wonderful lob beyond Aaron Butcher to double the advantage.
Coughlan missed the target with another chance in stoppage-time but there was no way back for the Fenmen.
4-3-3: Drury; Worthington, Stevens, Cartwright (sub Jackson 66 mins), Ward; Tidswell, Warfield (sub Coughlan 78 mins), Gale; Clitheroe, Ford, Thomas (sub Murrell 64 mins). Subs not used: Dougill, Roberts.
3-4-1-2: Butcher; Wilson, Cousins (sub Brand 74 mins), Fairweather; Watson, Millson, Hughes, Hipwell; Smith; Sparrow, Frew. Subs not used: Panayi, Di Cataldo, Cobb.
Ford pen (43 mins, 1-0); Coughlan (87 mins, 2-0).
Cartwright, Ford (kicking ball away); Wilson, Worthington, Hughes, Jackson, Fairweather (fouls).
Ollie Gale – inspirational display against his former club.