Martyn Wood and Joe Ford made just one change to their starting line-up, with Ryan Shaw coming in for Andrew Lawson on the wing.
Ford’s early penalty gave the visitors the lead, but it was soon cancelled out by Louis Grimoldby’s three-pointer for the hosts .
Ampthill scored their first try on 18 minutes through Jon Kpoku, improved by Grimoldby, but Carnegie hit back almost immediately when Tom Varndell and Tim Bitirim combined to send Dan Lancaster away. Ford missing the conversion.
Carnegie went back in front when a loose pass was gathered by former England winger Varndell and he raced away to score a try improved by Ford.
But the hosts upped their game as two tries in six minutes from Sam Baker put them in control, Grimoldby converting one.
Prop Aleki Lutui’s unconverted try made it 27-15 at the break.
Carnegie made a positive start to the second half and after 45 minutes they were in again.
Some strong attacking play saw James Elliott crossing and Ford was on target with the conversion.
But again Ampthill struck back straightaway with a try from hooker Dave Ward.
Both sides cancelled each other out for the next 20 minutes before the home side cut loose again to win the match.
After being camped deep in Carnegie’s 22, the ball came to Kpoku who crashed through two defenders to score under the posts and replacement fly-half Mickey Waters was successful with the conversion.
On 74 minutes replacement prop Matt Collins forced his way over, with Waters adding the goal.
Carnegie kept battling but conceded again when Waters passed to wing Nigel Baker who found Josh Gillespie and he scampered in untouched under the posts, to bring up the half-century.
Waters adding the goal for the final points of the game.