Blues are just one point down on Cornish Pirates, having lost 38-37 at The Mennaye in last week’s first leg.
Having led by 16 points midway through the first-half, Mike Rayer’s side will be massively disappointed not to have built on that, having not won in Cornwall since October 2018.
But it means there’s everything to play for in the return leg in front of their home crowd at Goldington Road.
For Ampthill the difference is ten points, after their game at Dillingham Park ended 31-21 in Ealing Trailfinders’ favour.
Ampthill will be looking to overturn that on their visit to the Championship title winners.
Head coach Paul Turner said afterwards: “It was a brave performance against the league champions.
"We’ve done lots of good things but its ultimately frustrating.
"I felt at half time despite being 7-19 down we could get back into the game if our set piece started to function.
"It did and we regained the momentum to get back to 21-24.
“Hereafter from the restart with 10 minutes to go we lost control tactically and with it the game.
"I couldn’t fault the effort but felt another one that got away against quality opposition.”
Both second-leg games kick off at 3pm, with Saturday being Ladies’ Day for Bedford Blues at Goldington Road.