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Boro missed a golden opportunity to go clear and were left in a four way split of the summit after losing at Forest.
Aitor Karanka's side were sole leaders at one point in the first half after they scrambled an opener when Grant Leadbitter's chip bundled in off the far post and defender Michael Mancienne.
But Forest levelled with a superb Gardner strike before the break then results eslewhere swung against them.
Boro dominated for long spells of the second half but despite plenty of possession and chances Forest broke clear for Dexter Blackstock to ram in the winner.
Then rivals Derby were pegged back by Birmingham to leave a log-jam on the whistle with Bournemouth, the Rams, Watford and Boro all on 66 points.
Boro stuck with the side that beat Millwall 3-0 in midweek and fielded an unchanged side for only the second time this season, the previous being the 3-1 win over Charlton.
Forest put on some early pressure but first Ben Gibson then Tomas Kalas nodded away quick knocks into the box towards Blackstock.
Boro's early probes were scrappy as a Lee Tomlin ball down the left was too far ahead of Albert Adonah then two long balls down the right towards ex-Forest man Patrick Bamford bounced out for throws.
But Forest almost snatched a freak opener on five minutes when a square ball found Antonio on the edge of the box and his low shot clipped Gibson on the heel then screwed up towards the far top corner sending keeper Dimi Konstantopoulos full length to his right to superbly claw it away.
Boro were pressing high up and almost got caught on 10 minutes when a long low diagonal ball skidded past the sliding blocking attempt of Kalas and sent Blackstock storming forward but the offside flag went up for what must have been a very close decision.
Boro almost picked their way through on 12 minutes as George Friend burst down the left and played a one-two with Adomah to get to the edge of the box where he was stopped by a firm tackle.
Then on 13 minutes a crisp move down the right found Tomlin who wriggled to the edge of the box but his well struck shot clipped Kike and deflected wide.
And two minutes later Adomah jinked in from the left to the edge of the box but his short square ball to Bamford was cut out by stretching defender Wilson then scrambled away.
Forest put in some heavy tackles as Kane clattered Bamford and Lichaj crunched Tomlin but both escaped punishment.
Boro went close on 18 minutes as Bamford peeled off his man to collect a Tomlin ball on the edge then drilled in a low angled effort that keeper Darlow did well to hold.
Boro almost got caught cold on 20 minutes as Antonio robbed Adam Clayton in midfield and raced forward. Kalas but in a sliding tackle that held the Forest man up and sent him wide to collect the loose ball then when he crossed towards Blackstock arriving in the middle alert Leadbitter cut it out.
And a minute later Antonio danced past Ryan Fredericks on the flank then scythed towards the box but again Kalas was on hand to steal it away as the wideman tried to check inside.
Then on 24 minutes Forest midfielder Lansbury carried the ball forward unchallenged only to blaze high over from 20 yards.
But Boro went ahead on 28 minutes as GRANT LEADBITTER sneaked down the right to the byline and as Forest backed off he edged goalwards then put in a chip that came back off the far post then looked to clip defender Mancienne on his back on its way in.
Forest hit back and almost levelled immediately as Burke got down the left and crossed in for Gardner to power a header just over.
And they were level on 34 minutes as GARY GARDNER neatly controlled a quick ball forward to bring it down then cracked in an unstoppable 25 yard shot that curled into the top corner beyond the dive of keeper Konstantopoulos.
Boro went close in a scramble on 37 minutes as first Bamford miscued a shot and the ball squirted inside to Kike who took an airshot and missed completely then when the loose ball fell for Friend he cut inside his man and cracked in a low shot that deflected goalwards forcing keeper Darlow to punch clear.
On 38 minutes Fredericks limped off after lengthy treatment to be replaced by Emilio Nsue.
Boro were quickly back on the attack as a quick break ended with Leadbitter firing over from 20 yards.
Leadbitter was booked for dissent after a Forest won a free-kick wide on the left on 43 minutes but the dead ball was easily collected by the keeper.
Nsue won a corner on the stroke of half-time and the delivery caused chaos in he box with Boro players appealing for a penalty as first Kike was hauled back then a rebound looked to have clipped a defender's hand but the ref waved play on.
HALF-TIME: FOREST 1 BORO 1
At the break Forest put on Osborn for injured Lansbury.
Boro showed first after the break as a quick ball forward on 47 minutes was held up well by Kike then a sharp exchange of passes sent Bamford into the box but his low shot cannoned back off a defender's shins then was hoofed clear.
Then Nsue tricked his way down the right and played a one-two with Tomlin to curl a cross towards the far post but Wilson out-jumped Kike and headed clear.
Then a hopeful stinging Leadbitter shot from 20 yards sent Darlow scampering across to save.
Then on 55 minutes a quick ball forward from Nsue was held up well by Kike who twisted and turned then slotted in to Tomlin but the ball was cut out.
Boro went close again on 57 minutes as Kike squeezed between two defenders to cut into the box from the right but his low shot was deflected behind off Lascelles for a corner.
And they went closer still on 59 minutes as Friend picked out Bamford to slot a ball into the box and Kike's back-heel bounced just wide of the post.
Then Friend surged forward and cut in to send a shot over.
Forest had a penalty shout waved away on 61 minutes as Antonio twisted round Nsue then flicked into a crowd and the ball looke dto have struck Kalas on the hand.
But Forest were back to take the lead on 65 minutes as Antonio broke down the left then cut inside and barged past Kalas then squared for DEXTER BLACKSTOCK to take a touch then turn and power a 12 yard shot past the diving keeper.
On 69 minutes Jelle Vossen replaced Adomah.
Boro had a lucky escape on 71 minutes as Konstantopoulos stretched to collect a cross and dropped it but in the tussle bwtween Kalas and Blackstock for the loose ball the referee spotted a push and gave a foul just as the Forest man looked to have won out.
Boro piled on the pressure as first a Tomlin shot was deflected behind then a string of corners were scrambled away nervously.
Boro had Forest penned in their own box for a long spell but were struggling to find the final ball.
Bamford picked out Tomlin in the box on 79 minutes but the 15 yard first time shot flashed a foot over the bar.
Then after a long spell trying to pick a way through Nsue crossed and Bamford nodded down but Kike just failed to connect six yards out and the ball bounced safely through to keeper Darlow.
On 81 minutes Boro put on Adam Forshaw for Leadbitter.
Forest won a throw on the right and went close on 82 minutes as Blackstock's looping 10 yard header drifted just wide.
Boro almost had a leveller on 83 minutes as Friend skipped past his man then cut into the box and squared for Kike but his stabbed shot from eight yards out rattled the outside of the post.
And Boro continued to press as first Bamford then Kike fired wide.
On 86 minutes Forest put defender Collins on for Blackstock.
Boro went close on 88 minutes as a speculative 25 yard Forshaw lob sent keeper Darlow back-pedalling to collect at the far post.
Then after a patient build up Nsue floated in a cross and keeper Darlow dropped it but it bounced just beyond Kike then was nervously scrambled awy.
In stoppage time Nsue was booked after losing the ball to Lichaj then chasing to bring the Forest man down.
BORO (4231): Konstantopoulos, Fredericks (Nsue 38), Kalas, Gibson, Friend, Adomah (Vossen 69), Leadbitter ( c) (Forshaw 81), Clayton, Tomlin, Bamford, Kike. Subs: Ripley, Whitehead, Reach, Woodgate
FOREST (4141): Darlow, Lichaj, Mancienne, Wilson, Lascelles, Gardner, Lansbury ( c) (Osborn, 46), Burke, Kane, Antonio, Blackstock (Collins, 86). Subs: De Vries, Veldwijk, Paterson, Vaughan, Walker.
Ref: Jonathan Moss (West Yorkshire)
Att: 24,200 (2,200 Boro fans)
