Gillingham must now beat Manchester City in the Wembley final on 30 May if they are to play in the top two divisions for the first time.
The Gills also began the match with the knowledge that they are one of only five clubs in the top three divisions never to have played at Wembley - the others being Barnsley, Walsall, Wrexham and the relegated Lincoln. Not that such a moderate history had stymied ambition. To judge from an investment brochure published by the club last week, a visit to the twin towers was intended to be just the start of a climb to the very top. "The Path to Premier League Football" noted that Gillingham's proximity to the Channel Tunnel made it "a prime location for a club to compete" in a putative European Super League.
First Preston, a club with a proud past as well as a hopeful future, had to be disposed of. The 1-1 draw at Deepdale in Sunday's first leg, the third such result between the teams this season, suggested the game would be tight but the explosive opening even outdid with the pre-match fireworks.
Preston kicked off but Gillingham quickly won possession, working the ball to Hessenthaler on the edge of the area. He played it in to Carl Asaba, burst unmarked into the box for the return, and drove the ball under the body of David Lucas.
The Preston goalkeeper, who was blamed for Bob Taylor's goal at Deepdale, was mortified but his team stayed calm, with Michael Jackson displaying their own goal threat as he headed over from David Eyres' corner.
Gillingham continued to press forward with Mark Patterson, Asaba and Taylor all winning corners with deflected shots and Taylor heading over from a good position. Lee Cartwright was booked as Preston sought to stem the tide but, while they did this, they were unable to test Vince Bartram seriously at the other end.
Preston were more dangerous in the opening 15 minutes of the second period with Ludden flashing a cross in front of goal, Jackson heading just over the bar after Gillingham had failed to clear a series of crosses, and John Macken stretching Bartram to his full length with a shot from 22 yards. However, they still introduced the barely fit 21-goal Kurt Nogan with 25 minutes left, forcing Gillingham further on the defensive.
Graham Alexander shot just over and Jason Harris fired wide as Preston continued to go forward. As the tension rose, with five frantic minutes of added time played largely in Gillingham's penalty area, a clutch of players were booked, but the Gills held on.
Gillingham (3-5-2): Bartram; Ashby, Pennock, Butters; Patterson, Hessenthaler, Smith, Galloway (Saunders, 54) Southall; Asaba (Hodge, 80), Taylor. Substitutes not used: Carr.
Preston North End (4-4-2): Lucas; Alexander, Jackson, Murdoch (Darby, 72), Ludden (Harris, 82); Cartwright, Gregan, Appleton, Eyres; Rankine (Nogan, 65), Macken.
Referee: M Halsey (Welwyn Garden City).