
The hosts paid for their profligacy in a tense shootout when, after the first 15 penalties had all been scored, United’s Anthony Elanga blazed over to send 9,000 Boro fans wild.
Jadon Sancho’s 25th-minute goal, shortly after Cristiano Ronaldo had missed a penalty, was scant reward for United’s dominance with Ronaldo and Marcus Rashford both culpable of failing to take golden chances.
Boro kept themselves in the tie, however, and equalised in the 64th minute when former United youth player Matt Crooks converted from close range.
Bruno Fernandes somehow struck the post with the goal gaping soon after and United then battered away at Boro’s defence in extra time all to no avail.
Boro then showed incredible poise with their penalties to send the 12-time FA Cup winners tumbling out.