United's U23s slipped to a first defeat of the season, losing out to Championship opposition in the Professional Development League on Monday.
Goals from Jordan Gabriel and Ben Brereton saw Nottingham Forest claim the spoils, after Tyler Smith had cancelled out Alex Lacovitti's opener at the City Ground.
The Blades were made to pay for missed opportunities after levelling proceedings, with Kimarni Smith and Shea Gordon wasting the best of the chances for the visitors.
Reflecting on the defeat and the need to improve defensively, Academy Manager Travis Binnion commented: "We started very well and for the first 20 minutes we were on top without capitalising on our dominance.
"Forest gradually took the game away from us and went ahead from a set-piece, but we hung on until half-time and re-grouped.
"Again we started brightly after the break and scored a good goal through Tyler (Smith), with him netting his fourth in as many matches, but instead of building on the equaliser Forest took the game away from us.
"Forest deserved the win and we gave away poor goals, which is unlike us and emphasises the need for us to work hard and improve moving forward.
Blades: Long, Charlesworth, Brown, J. Wallace (Graham 62), Cummings, Semple, T. Smith (Gilmour 58), Gordon, Hall, Hallam (Burton 78), K. Smith.
Unused: Perryman, Slater.