Gustavo Hamer scored a fine goal for Sheffield United but his efforts were in vain with Chris Wood coming off the bench to score the winner for Nottingham Forest.
Hamer curled in a fine effort from the edge of the box in the second half in what was a much-improved display from their opening weekend defeat to Crystal Palace despite a slow start.
Taiwo Awoniyi had given the hosts the lead with a neat header from Serge Aurier's cross, and Wood came on for the forward late on to replicate his efforts and earn Forest the win.