Second-half goals from Joe Lolley and Lewis Grabban helped Nottingham Forest end Middlesbrough's unbeaten home record and move into the Championship play-off places.
It marked a happy afternoon back on Teesside for former Boro boss Aitor Karanka, after his Forest side were beaten at the Riverside at the end of last season in his first return.
Both sides had chances in an open first-half but it was the visitors who made the breakthrough after the interval when Lolley took a pass from a driving Daryl Murphy and smashed a shot into the top corner for his third goal in four games.
Lolley had a further chance to add to the lead but was denied by Boro keeper Darren Randolph, while former Forest forward Britt Assombalonga was kept out at the other end by Costel Pantilimon's
Grabban made sure of the points when he turned in Lolley's cross at the near-post for his fifth goal in six, and not even the late dismissal of Jack Robinson, for a second yellow card for simulation, could stop Forest claiming the points.
Forest's victory, their fourth of the campaign, extended their unbeaten streak to six matches but, most importantly, ended a 12-game wait for three points on their travels.
Boro, whose success has been built on eight clean sheets and a solid defensive record, failed to score for only the fourth time this season as they slipped to their second league loss.