Match ends, Nottingham Forest 2, Middlesbrough 1.
Middlesbrough dropped to fourth in the Championship as Nottingham Forest came from behind to secure victory.
A draw for Boro would have been enough to move them top of the standings and they opened the scoring when Grant Leadbitter's cross ended up in the net.
Gary Gardner's superb strike from distance levelled matters before Dexter Blackstock's finish after a counter earned Forest the three points.
Boro are now level on 66 points with three other teams at the top.
Bournemouth lead the way by virtue of a better goal difference, while second-placed Derby surrendered a two-goal lead in injury time against Birmingham to draw 2-2 and Watford, third in the table, drew at Wolves by the same scoreline.
Boro had beaten Millwall 3-0 in midweek to move one point clear at the top and were looking to build on that with victory at the City Ground.
Forest, meanwhile, suffered their first defeat under Dougie Freedman against Charlton last time out and struggled initially against a confident Boro side.
The visitors had the better of the few chances in the opening stages as Lee Tomlin's deflected shot flew wide, before Patrick Bamford drew a save out of Karl Darlow.
However, they owed their opener to a huge slice of fortune as Leadbitter's cross into the area evaded everyone and looped into the net.
It was a deserved goal for Boro but Forest's response was swift as they equalised in stunning fashion, Gardner picking up the ball outside the box and superbly curling home from 25 yards.
From then on the game was much more even, with Kike shooting just wide for Boro, before Tomas Kalas had a penalty appeal waved away.
Forest who secured the three points when they broke quickly midway through the second half and Blackstock found space inside the area to fire in the winner.
Nottingham Forest manager Dougie Freedman: "I am delighted with the super-human effort the players showed.
"And I'm delighted with the response they produced to going behind, to suffering a set-back against the best team in the league, the strongest squad in the league and the one that will probably go on to win the title."
Middlesbrough manager Aitor Karanka: "We did not play well, we did not do the things that we said we had to do and we lost.
"This season will go right to the end, it will be close.
"But we have to be intelligent and we have to learn from this."
- 10LansburySubstituted forOsbornat 45'minutes
- 23BlackstockSubstituted forCollinsat 88'minutes
- 29de Vries
- 5FredericksSubstituted forNsueat 39'minutesBooked at 90mins
- 7LeadbitterBooked at 44minsSubstituted forForshawat 83'minutes
- 27AdomahSubstituted forVossenat 70'minutes
- Jonathan Moss
- Shots on Target
Second Half ends, Nottingham Forest 2, Middlesbrough 1.
Emilio Nsue Lopez (Middlesbrough) is shown the yellow card for a bad foul.
Foul by Emilio Nsue Lopez (Middlesbrough).
Eric Lichaj (Nottingham Forest) wins a free kick on the left wing.
Hand ball by Michail Antonio (Nottingham Forest).
Foul by Adam Clayton (Middlesbrough).
Michail Antonio (Nottingham Forest) wins a free kick on the left wing.
Corner, Nottingham Forest. Conceded by Ben Gibson.
Attempt saved. Adam Forshaw (Middlesbrough) right footed shot from outside the box is saved in the top right corner. Assisted by Adam Clayton.
Attempt missed. Kike (Middlesbrough) right footed shot from outside the box is high and wide to the right. Assisted by Lee Tomlin.
Attempt blocked. Lee Tomlin (Middlesbrough) right footed shot from outside the box is blocked. Assisted by Adam Clayton.
Substitution, Nottingham Forest. Danny Collins replaces Dexter Blackstock.
Attempt missed. Patrick Bamford (Middlesbrough) left footed shot from outside the box misses to the left. Assisted by Lee Tomlin.
Kike (Middlesbrough) hits the left post with a right footed shot from the centre of the box. Assisted by George Friend.
Substitution, Middlesbrough. Adam Forshaw replaces Grant Leadbitter.
Attempt missed. Dexter Blackstock (Nottingham Forest) header from the centre of the box misses to the right. Assisted by Eric Lichaj.
Attempt missed. Dexter Blackstock (Nottingham Forest) header from the left side of the six yard box misses to the left. Assisted by Chris Burke with a cross.
Attempt missed. Kike (Middlesbrough) right footed shot from very close range misses to the left. Assisted by Jelle Vossen.
Attempt blocked. Jelle Vossen (Middlesbrough) header from the centre of the box is blocked. Assisted by Emilio Nsue Lopez with a cross.