Aitor Karanka now knows he needs radical surgery on his struggling squad in January.
The Spanish boss was left simmering at his defence after watching bungling Boro concede a late sucker punch for the third game running.
Boro had dominated the second half but Brighton rocked them and plundered the points with a Matthew Upson header four minutes from time to win 1-0 at the Riverside.
Karanka has now been in charge of five games and in the last three he has seen the team repeatedly shoot themselves in the foot by leaking late goals from set plays.
At Derby, Boro battled back with ten men only to concedefour minutes in stoppage time and lose 2-1.
At Birmingham, Boro seemed to be cruising to a precious away win but were caught napping by a 90th- minute unchallenged header and had to settle for a 2-2 draw.
Then against Brighton they bossed the second half and piled on the pressure before again failing to deal with a routine corner.
Boro have thrown away five points in the closing stages of those three games and now find themselves suspended just three points above the drop zone.
For the first time Karanaka, a former Spanish international defender and Jose Mourinho’s right-hand man at Real Madrid, admitted he was angry.
He snapped: “We are giving gifts to our opponents in every game.
“We are finding it difficult to score but other teams are finding it very easy to score against us.
“You can say sorry one or two times but in five games, it’s the same mistakes. It is not possible to continue in this way.
“I can’t believe it. It is the same thing again. It is not normal to play so many games when you are probably better than your opponents but you do not get the points.”
Karanka has played as a defender at the highest level – he was won the Champions League with Real – but insisted the mistakes were fundamental.
He added: “At every level of football as a defender the most important thing at set plays is for a man to know who he is marking and to stop them from scoring goals.
“That is all. That is the job. And these players are not doing that job.
“It is always a lack of concentration. It can not continue in this way. Here we are again after five games now saying the same things.”
Karanka has already indicated he is eager to shuffle his pack when the January transfer window opens but before then Boro will need to improve dramatically if they are to avoid being sucked into the relegation battle.
They are now sixth bottom and just three points above the trapdoor having won just one game in seven.
Karanka said: “We are playing well for 85 minutes and then badly for five minutes.
“My wish to to concentrate in every game until the final minute.”
Brighton had the best of a lacklustre game at the Riverside and almost grabbed an opener on 10 minutes when Ashley Barnes put a header against the post after a corner then soon afterwards goalkeeper Shay Given had to back-pedal to tip a backward header from defender Jonathan Woodgate over.
Boro had first-half chances as first Mustapha Carayol brought a good save at the foot of the post then Rhys Williams and Jacob Butterfield had shots blocked.
After the break Boro took control and a George Friend shot from a tight angle was hacked off the line and when Carayol stabbed the rebound goalwards it was turned behind.
Then on 66 minutes Lukas Jutkiewicz put a diving header just over from an Albert Adomah cross.
Brighton snatched the points on 86 minutes as they won a disputed corner and when it dipped to the near -post Matthew Upson powered in a downward header which bounced up and inside the post.
MIDDLESBROUGH: Given, R Williams (L Williams 90), Woodgate (Gibson 46),Ayala, Friend, Adomah, Leadbitter, Whitehead, Butterfield, Carayol, Jutkiewicz (Main 72). Subs (not used): Konstantopoulos, Richardson, Smallwood, Haroun
BRIGHTON: Brezovan, Bruno, El-Abd, Upson, Ward (Calderon 75), Crofts, Bridcutt ©, Ince, Lopez (LuaLua 59), Barnes (Ulloa 82), Conway. Subs (not used): Walton, Andrews, Dunk, Agustien
Refereee: Mark Heywood (West Yorks) Att: 13,635.