United's youngsters cemented their position at the top of the U18s Professional Development League with a fifth success from six matches at the weekend.
A goal in each half from in-form striker Jordan Hallam paved the way for all three points over the U's, but as Lead Coach Derek Geary remarked it wasn't as comfortable as the scoreline looked.
But with his side top of the pile and having scored 21 goals in six outings to date, Geary beamed: "It's been a terrific start from what is a talented group of players.
"Credit to Colchester, they came and gave us a real tough test, they had long periods of possession and credited chances, but we defend well, remained resolute and managed the game very well.
"We are improving all the time and hopefully we're in for an enjoyable campaign; we have certainly started in the right manner."
In the opening exchanges there was good chances at either end, Perryman was alert to the danger to save well from a free-kick in the 13th minute, whilst at the other end Slater should have scored when clean through on goal, but he opted to pass to a team-mate when the better option appeared to shoot.
But in the 32nd minute, the Blades took the lead. In the second phase, following a free-kick, Gilmour got the ball onto the right-wing where Smith produced a pinpoint cross for HALLAM to expertly head home back across the goalkeeper.
The second period saw the visitors dominating possession for long spells without really troubling Perryman, the closest they came was from a shot on the angle from the left which went narrowly wide.
For United, substitute Mallon combined well with Gilmour before firing over, but with three minutes remaining HALLAM got his second to ensure all three points, sliding under the advancing goalkeeper with Smith again the provider.
Blades: Perryman, Portman, Charlesworth, Slater, Cummings, Ferguson, T. Smith (Allerton 84), Gilmour, Stewart (Ford 65) Hallam, Burton (Mallon 76)
Unused: Warhurst, Greaves.