England trio Wayne Rooney, Michael Carrick and Ashley Young all missed in the shootout, as the Boro players celebrated in front of their jubilant 10,000-strong travelling support.
In normal time, Stewart Downing's rasping drive for Boro was tipped over and Daley Blind put into his own net but striker Kike was flagged offside.
United's Jesse Lingard hit the post.
Middlesbrough will play Everton at home in the last eight, with the ties to be played in the week commencing 30 November.

Boro up to Premier League standard?

Middlesbrough last played in the Premier League in the 2008-09 season but Aitor Karanka's side, currently fourth in the Championship, held their own at Old Trafford, looking well organised at the back and managing to frustrate United throughout a goalless two hours.
Middlesbrough fans
The 10,000 travelling Middlesbrough fans shone their mobile phone lights on 10 minutes as a demonstration in support of the north east steel workers
Boro sat back and played on the counter-attack, Downing coming closest to winning it in normal time when he saw his effort kept out by keeper Sergio Romero.
When it came to penalties, Grant Leadbitter, Downing and Ben Gibson held their nerve to see the visitors through.

United fail to impress

Manchester United made nine changes to the side that drew against rivals Manchester City on Sunday.
But it was another slow, laboured performance by the Red Devils and they were unable to put concerted pressure on the Boro backline.
Wayne Rooney
Wayne Rooney had his penalty saved by Boro goalkeeper Tomas Mejias
Memphis Depay, left out in recent games, failed to impress on his return to the side, while striker James Wilson gave no impression that he could hold down a first-team place, replaced at half-time by captain Rooney.
Anthony Martial was also sent on by Louis van Gaal to provide more attacking impetus, but could not make the breakthrough.
Marouane Fellaini twice headed wide and Andreas Pereira flashed a shot wide, before United lost their fourth successive penalty shootout.

The stats you need to know

  • Manchester United have been knocked out by lower-league opposition in three of their last four League Cup meetings with sides from outside the top-flight
  • Before tonight, Middlesbrough had been eliminated in five of their last six League Cup meetings against Premier League opposition
  • Defeat means United have lost two of their last 15 League Cup ties at Old Trafford, both against Championship teams (Crystal Palace, 2011-12)

LINEUP, BOOKINGS (0) & SUBSTITUTIONS (6)

Manchester United

  • 20 Romero
  • 36 Darmian
  • 12 Smalling
  • 17 Blind
  • 05 Rojo (Young - 61' )
  • 16 Carrick
  • 27 Fellaini
  • 35 Lingard
  • 44 Pereira
  • 07 Depay (Martial - 71' )
  • 19 Wilson (Rooney - 45' )

Substitutes

  • 01 de Gea
  • 08 Mata
  • 09 Martial
  • 10 Rooney
  • 18 Young
  • 21 Herrera
  • 31 Schweinsteiger

Middlesbrough

  • 13 Mejias
  • 26 Kalas
  • 16 Stephens (Clayton - 114' )
  • 04 Ayala
  • 03 Friend
  • 06 Gibson
  • 07 Leadbitter
  • 24 Nsue
  • 10 De Pena (Zuculini - 78' )
  • 19 Downing
  • 09 Kike (Nugent - 84' )

Substitutes

  • 01 Konstantopoulos
  • 05 Amorebieta
  • 08 Clayton
  • 31 Fabbrini
  • 32 Jackson
  • 35 Nugent
  • 36 Zuculini
Ref: Lee Mason

MATCH STATS

Possession44%56%120minsManchester UnitedMiddlesbrough

Shots

137

On target

66

Corners

84

Fouls

127

Live Text Commentary

Full time
Full TimeMatch ends, Manchester United 0(1), Middlesbrough 0(3).
120:00+6:55
Penalty Shootout ends, Manchester United 0(1), Middlesbrough 0(3).
120:00+4:53
Penalty saved! Ashley Young (Manchester United) fails to capitalise on this great opportunity, right footed shot saved in the bottom right corner.
120:00+4:18Goal scored
Goal!Goal! Manchester United 0(1), Middlesbrough 0(3). Ben Gibson (Middlesbrough) converts the penalty with a right footed shot to the centre of the goal.
120:00+3:38
Penalty missed! Bad penalty by Michael Carrick (Manchester United) right footed shot is close, but misses the top right corner. Michael Carrick should be disappointed.
120:00+2:57Goal scored
Goal!Goal! Manchester United 0(1), Middlesbrough 0(2). Stewart Downing (Middlesbrough) converts the penalty with a right footed shot to the bottom right corner.
120:00+2:28Goal scored
Goal!Goal! Manchester United 0(1), Middlesbrough 0(1). Andreas Pereira (Manchester United) converts the penalty with a right footed shot to the bottom left corner.
120:00+1:55
Penalty missed! Bad penalty by David Nugent (Middlesbrough) right footed shot is close, but misses the top right corner. David Nugent should be disappointed.
120:00+1:19
Penalty saved! Wayne Rooney (Manchester United) fails to capitalise on this great opportunity, right footed shot saved in the bottom right corner.
120:00+0:31Goal scored
Goal!Goal! Manchester United 0, Middlesbrough 0(1). Grant Leadbitter (Middlesbrough) converts the penalty with a right footed shot to the top right corner.
120:00Penalty shootout
Penalty Shootout begins Manchester United 0, Middlesbrough 0.
120:00+0:59
Second Half Extra Time ends, Manchester United 0, Middlesbrough 0.
120:00+0:47
Attempt missed. Marouane Fellaini (Manchester United) header from the centre of the box is just a bit too high.
119:42
Attempt missed. Anthony Martial (Manchester United) header from very close range is close, but misses to the left.
118:26
Attempt missed. Marouane Fellaini (Manchester United) header from the centre of the box is close, but misses to the left.
117:47
Corner, Manchester United. Conceded by Stewart Downing.
115:30
Attempt missed. Andreas Pereira (Manchester United) right footed shot from outside the box is close, but misses to the left.
113:31Substitution
SubstitutionSubstitution, Middlesbrough. Adam Clayton replaces Jack Stephens.
109:53
Emilio Nsue Lopez (Middlesbrough) wins a free kick in the defensive half.
109:53
Foul by Ashley Young (Manchester United).