Steve Sidwell scored a last gasp goal to frustrate those still in attendance at the City Ground to give the promotion chasers a 2-1 victory.
Dexter Blackstock scored Forest's goal after coming on as a substitute late in the first half for the injured Jamie Ward, with the side having to re-adjust tactically.
Blackstock seemed to have a positive impact, and his performance was lauded after the game in the SkySports studio.
Former Blackpool and Crystal Palace boss Ian Holloway told the channel: "They are a better team with him (Blackstock) in it. The manager's made his choices but they looked better team in second half."
His assessment was echoed by ex-Forest boss Steve Cotterill, who previously managed Blackstock at the City Ground.
He told SkySports: "He (Blackstock) changed the game, and brought Lansbury into the game, Lansbury was tremendous."
Unfortunately for Forest it was a promising performance, which yielded no reward. They have told all four games under Williams, but remains seven points clear of the relegation zone with five games to go.