Two goals in a minute with the clock ticking down brought a victory which had begun to look unlikely.
And they had teenager Kyle Naughton and new signing Darius Henderson to thank for the win.
Hard working Huddersfield had been keen to avoid their own fans getting on their back after losing 3-1 at home to MK Dons in League One last weekend.
They are without a win in that division and are next to bottom.
Their only success had become at the start of this month, when they trounced Bradford City 4-0 in the earlier round of the Carling Cup.
United, on the other hand, are in buoyant fifth spot in The Championship and have hit nine goals in their last three games, an early-season run which included their Carling Cup win over Port Vale.
Yet United went behind after 34 minutes after a period of possession and pressure from the home team.
Michael Flynn, a busy, 27-year-old attacking midfielder, surged forward to beat Bennett in the Blades' goal.
An out of sorts Jonathan Stead and David Carney started trying to force open the home defence, with little success.
Stead was taken off after the interval and Danny Webber became a thorn in Town's side.
It looked like a shock could be on the cards until the towering presence of Henderson levelled on 82 minutes.
It was a fitting reward for some hard work for the Doncaster-born striker.
Then 19-year-old Naughton, who had come on for Carney, rocked the West Yorkshire with a deflected winner a minute later. He fired a right footer from inside the penalty area.
Huddersfield: Glennon, Holdsworth, Clarke, Parker, Worthington, Cadamarteri, Flynn, Williams, Roberts, Beckett, Lucketti. Subs: Skarz, Collins, Kamara, Jevons, Goodwin, Unsworth, Smithies.
Blades: Bennett, Cotterill, Morgan, Kilgallon, Henderson, Stead, Sun, Carney, Tonge, Spring, Geary.
Subs: Kenny, Webber, Montgomery, Sharp, Robertson,
Naughton, Ehiogu.
Full report and pictures in Thursday's Star.