A Richard Blythe double made it four wins on the bounce for Town from a game that lacked any real quality at Butlin Road.
The midfielder struck a goal in each half for a Rugby side that ended the encounter a player light following the 83rd minute dismissal of substitute Stefan Blake.
Valley boss Carl Adams had named an unchanged starting line-up, although there was a place on the bench for new signing Romario Martin - with summer recruit Simeon Tulloch also featuring in a matchday squad for the first time.
It was once more a confident start by Adams's men, and they were soon ahead when Danico Johnson showed good strength in the box to hold the ball up well before teeing up Blythe for a composed finish.
The visitors' first chance of the half came when Josh Ford found some space down his side's right, but he could only shoot straight at Matt Hill in the Town goal.
Stacey Cartwright's free-kick drifted just wide of the target, as United continued their search for an equaliser, whilst at the other end Keenah Rosser's low cross just failed to reach a team mate.
Valley nearly doubled their advantage after Lewis Rankin had shown great skill to beat his marker on the byline and then play the ball to Justin Marsden, but his goalbound shot appeared to strike a Holbeach hand.
Unfortunately referee Sam Anderson did not share this view and rejected Town's loud appeals for a penalty.
More strength from Johnson's at close quarters created a further opportunity for the hosts, but his effort was smothered away, with the final attempt of the opening period coming when Ford again got free - but his volley on the turn was well-saved by Hill.
Ford had the first chance of the new half too when he pounced on a poor defensive header by Dominic Perkins, but the Rugby defender instantly made amends for this with a strong block to the resulting strike.
Debuting United keeper Joe Tarris did well to palm away Johnson's deflected shot and Marsden's pull-back from the left hand side went behind its intended targets, as the home side got back into their stride post-interval.
This renewed impetus from Valley saw two decent chances go begging, with first Blythe stabbing one wide after Johnson had picked him out from the left, and then Richard Bunting failing to get a true connection on a Marsden cross from the same wing.
However Blythe did make the game safe on 71 minutes when he rolled the ball home after Johnson had got up from being fouled on the edge of the box to execute a quick free-kick which ultimately looped up past Rankin into the goalscorer's path.
Neither side really threatened again from there on, with the focus of the action being on the match official Anderson, who dished out a red card to Blake within ten minutes of his arrival to the game from the bench after his late tackle on Jon Clay had led to a player melee in front of the main stand.
Holbeach's Spencer Tinkler escaped the same punishment shortly after though, despite appearing to stamp on Rankin after he had fouled the Rugby man.
Line-up: Hill; Rosser, Perkins, Recci, Edwards; Blythe, Bunting (Blake), Marsden (Martin); Rankin, Evans (Tulloch), Johnson. Subs not used: Adams, Kavanagh.
Evesham line-up: Tarris, T.Smith, Cartwright, Clay, Brathwaite, Jackson, Avis, Tinkler, Ford, J.Smith, W.Smith. Subs: Hamilton, Harker, Barker, Whyatt, Kirk.