The home side dominated the match for long periods but were unable to make the breakthrough they deserved after falling behind to a third minute Marcus Richardson penalty.
The Lambs' cause was not helped by the second half dismissal of Matty Williams for violent conduct but, even when reduced to ten men, the home side controlled proceedings and could count themselves unlucky not to earn at least a point.
Tamworth boss Mark Cooper was forced to make changes from the side which lost 2-0 at Altrincham the previous week.
In came Matty Williams, Emmet Friars, John McGrath and Graeme Law with the suspended Bradley Thomas, injured duo Joe Kendrick and Jon Stevenson plus Paul Devlin the men to make way.
Cambridge United were unchanged from the side which claimed victory over Aldershot eight days before.
The visitors got off to a flying start as Tamworth defender Emmet Friars was adjudged to have brought down Liam Marum in the penalty area on three minutes. Richardson confidently stroked away the resultant spot-kick.
The home side responded by forcing a couple of dangerous free-kicks on the edge of the United box, but it was Marum who almost doubled the Cambridge lead on eight minutes, turning neatly inside the area before firing narrowly wide.
From that point on the first half was one-way traffic as the home side repeatedly pressed for an equaliser. The Lambs almost levelled on 11 minutes as Taiwo Atieno beat the off-side trap but saw his low show pushed clear by Paul Crichton.
Tamworth began to look more threatening as John McGrath saw a free-kick deflected away for a corner while Williams saw a header gathered comfortably by Crichton.
Williams found himself in a dangerous position again on 18 minutes but blazed wide under pressure from Michael Morrison.
Tamworth should have levelled a minute later but Tom Kemp directed his header well wide from close range. Kemp had a second chance to level the scores soon after but headed McGrath's free-kick over the bar.
Atieno should have equalised for Tamworth on 32 minutes scuffing a shot wide inside the area after collecting a long ball from Friars. The former Walsall striker missed another good chance on 39 minutes, heading a McGrath free-kick wide from six yards.
Tamworth continued to look lively at the start of the second half but Matthew Bloomer almost headed Cambridge into a 2-0 lead on 51 minutes as his effort sailed just over the bar.
Jon Brady saw a 35-yard speculative shot go just over for the visitors while, at the other end, McGrath was denied by Crichton.
The Lambs continued to pile on the pressure and Adie Smith saw a shot blocked as Cambridge battled to defend their lead.
Williams had the ball in the net on 61 minutes but was adjudged to be off-side. Two minutes later, the former Notts County striker's afternoon went from bad to worse as he was handed a straight red for lashing out at Morrison.
Cooper threw caution to the wind by bringing on striker Steve Burton for midfielder Kyle Storer and, despite being down to ten men the Lambs continued to have the greater share of possession.
Cambridge substitute Stephen Smith headed a Brady cross wide, while visiting keeper Crichton had to be alert to deny a long range effort from Tamworth substitute Michael Touhy effort on 82 minutes.
McAllum whipped in a cross-shot late on which was well handled by Crichton. It proved to be the last real throw of the dice for the home side despite five minutes of injury time.