On-loan pair Andraz Sporar and Onel Hernandez opened their Middlesbrough accounts as a debut howler from Nottingham Forest goalkeeper Ethan Horvath piled more pressure on boss Chris Hughton.
United States international Horvath, a summer signing from Club Brugge, badly miscontrolled a backpass to let Hernandez steal in to seal the points and keep Forest rooted to the foot of the Championship.
Slovenia striker Sporar, a transfer deadline day capture from Sporting Lisbon, had crashed home an emphatic finish midway through the first half to put the visitors ahead on his first Boro start.
Victory, Boro's first in five matches, moved Neil Warnock's side up seven places to 11th, while Forest have just one point to their name after a sixth defeat in seven matches.