The 90 minutes had been largely an uneventful affair with few chances to entertain the TV audience or warm up the few in the stadium.
But in sub-zero temperatures, it was substitute McTominay who eventually turned the heat up with a 97th-minute strike.
Our Scotland international had come on for Nemanja Matic after 73 minutes and scored his third in three matches following efforts against Southampton and Everton, and won it 1-0 for the Reds to send us into Thursday night’s last-eight draw.
FIRST HALF - ALL SQUARE BUT REDS ON TOP
It was a quiet start to the tie but United were dominant in terms of possession and created the opening two chances of the match.