Hereford'S hopes of a first ever FA Umbro Trophy final were eclipsed inside half an hour of Saturday's second leg at Edgar Street.
By then, the unfancied visitors were two goals to the good, although the Bulls had had much the better of play.
But a combination of brilliant goalkeeping by Green's Steve Perrin, United's on-going failure in front of goal, and the contribution of the influential Frankie Bennett put Green well on the way to their second final in three years.
Perrin flew through the air to clasp Ian Wright's well-struck 20-yarder with just three minutes played and then, after watching Paul Sturgess's 35-yarder skid well wide, held on to a Phil Robinson header after Rob Elmes had flicked on a Matt Clarke throw.
Little had been seen of Forest Green in the early exchanges but, in contrast to Hereford, the visitors grabbed the first chance that came their way.
Bennett seized on a Stuart Slater cross and drove an unstoppable shot past Scott Cooksey from the edge of the penalty area.
Wright headed a Gavin Williams cross just wide, Perrin saved brilliantly from Jimmy Quiggin and Robinson saw a goal-bound shot blocked by Billy Clark before Green extended their lead on 28 minutes.
Bennett went flying by Sturgess on the right and his cross was headed against an upright by Adrian Foster with the rebound falling for Alex Meechan who despatched the loose ball.
By this stage, Hereford had had eight goal attempts, Green two, but the scoreline told its convincing story.
Further fine saves by Perrin followed from Elmes and Robinson before the break and the United player-coach might have done better with a 53rd-minute effort which he side-footed weakly at the keeper.
But by 59 minutes United's dreams were firmly and finally crushed when Chris Burns hit the third from close range after the United defence failed to clear a Slater corner.
Wright headed in a Williams corner three minutes later to raise a glimmer of hope but this was emphatically snuffed out on 81 minutes when Foster, returning like Banquo's ghost, drilled home an excellent shot from 20 yards after a fine run and pass by Slater.
So, after eclipsing the favourites 6-3 on aggregate over the two legs, Forest Green earned a place in the final against Canvey Island who gained a repeat 2-0 win over Chester in the second leg.
Hereford: Cooksey, Clarke, Sturgess, Robinson, Wright, James, Quiggin, Snape, Elmes, Williams, Parry (Bull 64 mins). Subs not used: Baker, Wall, Giddings, Shirley.
Forest Green: Perrin, Cousins, Lockwood, M Foster, Clark, Burns, Bennett, Drysdale, A Foster (Daley 84 mins), Meechan, Slater. Subs not used: Price, Allen, Hunt, Ghent.
Referee: D Pugh (Wirral).
Attendance: 4,175.
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