Despite the tight scoreline, it was a game Adrian Forbes’ side controlled throughout and took advantage of from 12 yards after Trialist B was brought down in the area.
It was a competitive start at the Premier Plus Stadium in St Neots with the first chance falling to Tyrelle Newton, who after combining well with TQ Addy, fired goalwards first time only to be denied by the Cambridge keeper.
Aidan Francis-Clarke was alert to looming danger minutes after as the home side had a chance of their own, but for the outstretched leg of the centre-back thwarting an effort on goal.
Momentum shifted Town’s way once again midway through the first period as Tra Lucas produced a stunning flick over his opposite number, progressed down the right-hand-side and crossed aiming for Addy, who was inches away from making contact and heading the Hatters ahead.
Addy was at the forefront of the action again minutes later as he found himself with space to shoot, but he dragged his right-footed shot just wide of the target.
The tricky winger was twice unlikely at the beginning of the second half, with the keeper producing a find save to his left-hand-side, before Addy missed the target with a promising opportunity.
The breakthrough wasn't long after though which came from the penalty spot. Trialist B was fouled in the area and Allen stepped up from 12 yards and found the bottom corner.
Trialist B was a regular threat for Cambridge to try and contain, even coming close to a goal himself in the 90th minute but he failed to convert Addy’s cut-back.
Town: Horlick; Odell, Francis-Clarke, Williams; Nicolson, Pettit (C), Newton, Trialist A; Lucas (Trialist B), Addy, Allen.
Subs not used: Cowler, Heron, Pinnington, Bateson.
Goals: Allen (56’)