BURNLEY slipped to a second defeat in five games after conceding twice in the second half.
Dexter Blackstock gave Nottingham Forest the lead after a goalless first half, despite appearing to foul Jason Shackell in the process of climbing to head in the opener just before the hour.
The Clarets almost conjured an immediate equaliser but Charlie Austin's shot from inside the box was well parried by goalkeeper Lee Camp, and Dean Marney's follow-up was blocked.
Sam Vokes replaced Brian Stock, and after scoring twice from the bench in the previous five games – including the equaliser in last week's derby draw with Blackburn Rovers – the Welsh striker almost repeated with feat soon after his 65th minute introduction.
Austin put an excellent ball into the box, but Vokes glanced narrowly wide.
Forest were looking for a response after losing their last two games, and Billy Sharp put the result virtually beyond doubt after beating the offside trap and slotting across Lee Grant into the bottom right corner.
Junior Stanislas, a 73rd minute substitute for Martin Paterson, who had been denied by the post in the first half, fired a free kick for a foul on Chris McCann on target, but Camp scooped it up.