The Yellows continued their indifferent form of late as they had no answer to a dominant defensive performance by the visitors, who then made the most of their chances at the other end.
Second half goals from Stefan Galinski, Danny Meadows and Jordan Hempenstall fired Grantham to a final meeting with Ashton United on Saturday.
In truth, the Yellows had been limping to the end of the season in poor form and without several players and their squad finally broke at the death.
Already missing the likes of captain James McCarten, Dylan Vassallo, Liam Hynes and Tony Gray, as well as the suspended Rory McKeown and Mekhi Leacock-McLeod, the Yellows were dealt a further blow when Shaun Beeley withdrew due to a family bereavement.
A bumper crowd of 737 attended Cantilever Park to witness a cagey opening quarter as both sides tried to get the upper hand.
Neither side could carve out much of an opening, though Lee Shaw perhaps would have liked to have done better with a chance when he was released by a good ball through the middle.
At the other end, the Yellows lacked creativity throughout and the only real dangerous moment Kieran Preston had, was when he was forced to shimmy past two attackers from a back pass.
It remained cagey and niggly at the start of the second half and the Yellows had a first real sight of goal when a cross from the left fell to substitute Stephen Milne at the back post, and his shot was charged down and went behind for a corner.
The visitors would break the deadlock on 59 minutes, a half cleared free-kick made its way back in to the box and as the ball bounced around, it popped up for the excellent Galinski who beat Luke Pilling to it to divert home.
Warrington still struggled to carve out openings and the lead gave the visitors momentum and they went for the kill.
The crucial second goal came on 70 minutes, and again via a deflection. A free-kick was won by Oliver Luto in his own half, and from it the ball bounced around before Meadows steered it home via a deflection.
It wasn’t to be Warrington’s night and Grantham added more gloss to the scoreline with a fine third goal, Hempenstall heading home from the edge of the box in to the top corner.
It brings an abrupt end to what had been a successful season for the Yellows, who had enjoyed a tremendous FA Trophy run and also achieved the aim of making the play-offs, but sadly they ran out of steam and will remain in the Evo-Stik Premier League in 2018/19.
Warrington Town: Pilling, Carden, McEveley (Milne), Jennings, Higgins (Makinson), Goulding, Kinsella, Williams, McDonald, Piggott, Hayhurst. Unused subs: Barnes, Davis, Bakare.
Grantham Town: Preston, Potts, Luto, Hollingsworth (Lewis), Galinski, Batchelor, Meadows, Wright (McGovern), Hempenstall (Hakeem), Shaw, Burrows. Unused subs: Osbourne, Vince.