Two goals in the first 5 minutes after the break made the Gingerbreads job hard and a red card for Ross Barrows after an hour sealed the game for the home side.
"The message at half time was to keep doing what we had, but five minutes after the break we've conceded two quickly again." Said Gingerbreads Manager Richard Thomas. "We were chasing things from that moment which was always going to be tough."
A feisty first half kicked off with players and benches squaring up after Tony Gray tangled with Tom Ward. No cards were shown despite an apparent stamp, but the tone was set for the rest of the game.
From the first whistle, the home side pressed Grantham, but found the Gingerbreads in resilient mood. After 11 minutes, Jack Dunn made space to fire in a shot. Jordan Wright turned it onto the post and gathered the ball.
Dunn set up Gray seven minutes later. The strikers low shot was well saved by Wright. The home side continued to create the best chances and went close again on 31 minutes. Ben Garrity got a header to a corner, but Chris Salt was in the right place to clear the Gingerbreads lines.
Grantham only made half chances that Danny Durkin and Kevin Hemagou could only drag wide. As the half drew to a close, Dominic Reid made some space just outside the Grantham penalty area, but rolled his shot at Wright.
The first five minutes of the second half gave the Gingerbreads an uphill challenge. There was only a minute gone when Alex Whittle skipped past the right hand side of the Grantham defence and delivered a cross to the near post. Amis timed his run to get there before Wright and head home the opening goal.
Gray twice set up Amis in the next few minutes. The Warrington striker grabbed his second of the game after 50 minutes, getting on the end of a through ball from Gray and slipping the ball past Wright.
With an hour gone, the Gingerbreads uphill challenge became a mountain climb. A trip in the centre of the pitch earned Ross Barrows a second yellow card and gave Grantham half an hour to face with ten men.
A Hemagou snap shot after 66 minutes almost got Grantham back into the game, but his effort was deflected wide of the post. Warrington added a third goal with 20 minutes left. Reid outpaced the Gingerbreads defence onto a through ball. Wright came out to challenge him, but the ball fell to Amis who rolled it into the empty net for his hat-trick.
With Grantham up against it for the remainder of the game, the home side created four quick chances. Gray, Reid, Amis and Whittle all went close, but a combination of saves from Wright and poor finishing stopped the home side adding to their lead.