A deflected strike from Dutchman Marvin Emnes earned Middlesbrough their fourth successive away win - in manager Tony Mowbray's 100th match in charge.
Striker Emnes, 24, saw his first-half attempt from the edge of the area take a huge deflection to wrong-foot Brighton keeper Tomasz Kuszczak.
Brighton carved out chances but Boro keeper Jason Steele thwarted Ashley Barnes with an excellent save.
Craig Mackail-Smith then spurned a glorious late chance.
Having gone top of the table after five straight league wins earlier in the season, Brighton have lost their way.
Manager Gus Poyet will be concerned his side, who netted 14 times in that winning sequenece, have only scored once in four games.
In contrast, Boro have now won their last two games.
Former England defender Jonathan Woodgate, 32, typified his team's battling performance with a brave block which denied Brighton's David Lopez a goal.
Boro looked dangerous on the counter-attack, and Emnes silenced the home crowd by making the breakthrough with a fortunate effort.
Brighton tried to hit back and went close through a Dean Hammond header before Mackail-Smith headed over.
Brighton boss Gus Poyet: "It's painful really. Right now we are not scoring. We have the best defence in the Championship yet we can't win.
"It is up to us. It's a team problem in terms of how many chances you create. We only have ourselves to blame for not scoring.
"In our recent home games we have had chances to win easily. If the players were not trying I would be very upset. The only thing you can ask is for them to put the ball in the net."
Middlesbrough boss Tony Mowbray: "You have to prepare properly to face Brighton as they have an exceptionally good side.
"They are going to be frustrated but I'm sure they will have a good season. They will be there or thereabouts.
"We had a lot of the ball early on and Brighton came at us as the game wore on and hopefully we'll get stronger.
"The Championship is a very tactical league, there are some good coaches in it and it's not a crime to put men behind the ball."
- 29 Kuszczak
- 02 Bruno
- 03 Greer Booked
- 06 El-Abd (Dobbie - 69' )
- 28 Bridge
- 04 Hammond
- 08 Crofts (Buckley - 69' )
- 21 David Lopez (LuaLua - 82' )
- 26 Bridcutt
- 09 Barnes
- 12 Mackail-Smith
- 16 Ankergren
- 05 Dunk
- 14 Calderon
- 18 Dicker
- 25 LuaLua
- 30 Buckley
- 10 Dobbie
- 01 Steele
- 03 Amougou
- 04 Friend
- 21 Parnaby
- 39 Woodgate
- 07 Leadbitter
- 10 Bailey
- 16 McEachran (Miller - 73' )
- 38 Haroun
- 09 Emnes (Smallwood - 80' )
- 27 McDonald Booked (Reach - 85' )
- 32 Leutwiler
- 15 Hines
- 25 Reach
- 08 Thomson
- 33 Smallwood
- 11 Ledesma
- 30 Miller
Live Text Commentary
Full Time The referee ends the match.90:00 +2:50
Kazenga LuaLua has shot on goal from just outside the area which goes wide of the right-hand upright.90:00 +1:12
Wayne Bridge concedes a free kick for a foul on Grant Leadbitter. Direct free kick taken by Grant Leadbitter.88:35
Faris Haroun concedes a free kick for a foul on Ashley Barnes. Liam Bridcutt takes the direct free kick.86:57
Stuart Parnaby concedes a free kick for a foul on Kazenga LuaLua. Direct free kick taken by Wayne Bridge.86:52
Effort from deep inside the area by Ishmael Miller misses to the left of the goal.84:33 Substitution
Substitution Adam Reach joins the action as a substitute, replacing Scott McDonald.83:15
Free kick awarded for a foul by George Friend on Will Buckley. Liam Bridcutt takes the free kick.81:16 Substitution
Substitution Kazenga LuaLua on for Moreno David Lopez.79:43 Substitution
Substitution Marvin Emnes leaves the field to be replaced by Richard Smallwood.78:23 Booking
Booking Caution for Gordon Greer.77:55 Booking
Booking Scott McDonald is cautioned.75:51
Will Buckley takes a short corner.74:49
Will Buckley gives away a free kick for an unfair challenge on Nicky Bailey. Grant Leadbitter crosses the ball from the free kick right-footed from left channel.74:07
Inswinging corner taken right-footed by Grant Leadbitter from the left by-line, clearance made by Ashley Barnes.73:49
Effort from 25 yards by Grant Leadbitter. Tomasz Kuszczak makes a save.72:09 Substitution
Substitution Ishmael Miller joins the action as a substitute, replacing Josh McEachran.71:27
Stephen Dobbie takes a shot. Comfortable save by Jason Steele. Effort on goal by Stephen Dobbie from inside the box misses to the right of the target.70:04
Ashley Barnes takes a shot. Save made by Jason Steele. Will Buckley has an effort at goal from deep inside the area missing to the right of the target.68:23 Substitution
Substitution Stephen Dobbie joins the action as a substitute, replacing Adam El-Abd.
Substitution Will Buckley on for Andrew Crofts.67:22
Stuart Parnaby concedes a free kick for a foul on Wayne Bridge. Free kick taken by Wayne Bridge.66:48
Effort by Ashley Barnes from a long way out goes over the target.64:57
Effort from deep inside the area by Andrew Crofts misses to the left of the goal.61:08
Moreno David Lopez takes a shot. Jonathan Woodgate gets a block in. Ashley Barnes takes a shot. Jason Steele makes a save. Craig Mackail-Smith produces a header from deep inside the six-yard box that clears the crossbar.60:16
Wayne Bridge fouled by Stuart Parnaby, the ref awards a free kick. Free kick crossed by Moreno David Lopez, clearance made by Jonathan Woodgate.59:13
Craig Mackail-Smith concedes a free kick for a foul on Jonathan Woodgate. Free kick taken by Josh McEachran.57:44
Josh McEachran challenges Dean Hammond unfairly and gives away a free kick. Liam Bridcutt takes the direct free kick.56:23
Liam Bridcutt challenges Scott McDonald unfairly and gives away a free kick. Jason Steele restarts play with the free kick.55:00
Bruno Saltor fouled by Scott McDonald, the ref awards a free kick. Gordon Greer takes the free kick.52:34
Free kick awarded for a foul by Liam Bridcutt on Scott McDonald. Nicky Bailey restarts play with the free kick.49:30
Liam Bridcutt challenges Faris Haroun unfairly and gives away a free kick. Josh McEachran takes the free kick.45:01
The second half has started.45:00 +1:11
Corner taken by Moreno David Lopez from the right by-line, clearance made by Faris Haroun.45:00 +0:31
Liam Bridcutt fouled by Faris Haroun, the ref awards a free kick. Adam El-Abd takes the direct free kick.44:17
Scott McDonald gives away a free kick for an unfair challenge on Wayne Bridge. Moreno David Lopez crosses the ball in from the free kick, clearance made by Jonathan Woodgate.43:16 Half time
Half Time The ref blows to end the first period.40:41
Shot from outside the area by Wayne Bridge misses to the left of the goal.39:07
Craig Mackail-Smith has an effort at goal from outside the penalty area which goes wide right of the goal.37:56
Free kick awarded for an unfair challenge on Scott McDonald by Bruno Saltor. Free kick crossed right-footed by Grant Leadbitter from left channel, clearance made by Liam Bridcutt.34:18
Andrew Crofts produces a header from inside the area that goes over the bar.32:10
Moreno David Lopez challenges Josh McEachran unfairly and gives away a free kick. Direct free kick taken by Josh McEachran.31:31
Free kick awarded for an unfair challenge on Marvin Emnes by Dean Hammond. Grant Leadbitter takes the direct free kick.31:06
Free kick awarded for an unfair challenge on Faris Haroun by Dean Hammond. Free kick taken by Nicky Bailey.29:25
Inswinging corner taken by Moreno David Lopez from the right by-line, Bruno Saltor has an effort at goal from outside the box which goes wide right of the target.29:08
Craig Mackail-Smith takes a shot. Save made by Jason Steele.27:06
Corner taken right-footed by Moreno David Lopez from the left by-line, Dean Hammond has a headed effort from close in and clears the bar.26:07
Foul by George Friend on Ashley Barnes, free kick awarded. Moreno David Lopez restarts play with the free kick.23:49
Corner taken by Grant Leadbitter from the left by-line, Tomasz Kuszczak makes a save.23:24
Faris Haroun takes a shot. Gordon Greer gets a block in.20:30 Goal scored
Goal! - Marvin Emnes - Brighton 0 - 1 Middlesbro Marvin Emnes gets on the score sheet with a goal from just outside the penalty box to the bottom right corner of the goal. Brighton 0-1 Middlesbrough.18:54
Outswinging corner taken from the right by-line by Moreno David Lopez.10:54
Inswinging corner taken by Moreno David Lopez, save made by Jason Steele.10:22
Outswinging corner taken by Moreno David Lopez, clearance made by Jonathan Woodgate.8:58
Moreno David Lopez takes the inswinging corner, clearance made by Nicky Bailey.0:00
The game kicks-off.
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