Grant Leadbitter's goal after 67 minutes gave Aitor Karanka's unfancied visitors a surprise advantage until Anthony Martial swept home on 85 minutes and Paul Pogba won it 87 seconds later with a fine header
Manchester United manager Jose Mourinho saluted the Old Trafford crowd and said they swept his side to a dramatic 2-1 victory over Middlesbrough.
Grant Leadbitter's goal after 67 minutes gave Aitor Karanka's unfancied visitors a surprise advantage until Anthony Martial swept home on 85 minutes and Paul Pogba won it 87 seconds later with a fine header.
The late turnaround -- reminiscent of the glory years of the watching Alex Ferguson on his 75th birthday -- sealed United's fifth consecutive Premier League victory and they are now unbeaten in 12 matches in all competitions.
A delighted Mourinho believes the atmosphere inside the "Theatre of Dreams" eventually made all the difference.
"We managed to do something that is amazing, which is to bring the fans onto the pitch," he said.
"I think we did that in the last 15 and 20 minutes. We played with 70,000 or 80,000. What was on the pitch was too much for a very good team.
"I feel for my brother (Karanka) but not just him, I feel for their players because they gave it everything. But my players deserved it because they gave it everything."
United should have been out of sight by half time after dominating the first 45 minutes.
They hit the post twice, courtesy of Pogba and Martial, and Zlatan Ibrahimovic also had a goal controversially ruled out.
If Ibrahimovic's goal had been allowed to stand he would have matched Lionel Messi's 2016 tally of 51 strikes in the calendar year and Mourinho was upset that the 35-year-old was denied the chance of equalling that record.
"That stopped such an amazing player from being top scorer with Messi in 2016. It was quite frustrating and it was another big test for us and the players."
After the break United remained in complete control but Middlesbrough's resilience was superb as they repelled constant United attacks, until Martial and Pogba produced the goods in an end that was extremely cruel on the visitors.
"If the fans remember Sir Alex, not just for his birthday but for the performance we had, that is a great tribute," Mourinho said.
"I think the fans love the way we try and play football and they love the players' attitude. It was a big victory for us, a big three points."
Karanka was Mourinho's assistant for three years from 2010 at Real Madrid and the United manager spoke in his pre-match programme notes of his genuine affection for his Middlesbrough counterpart.
Karanka feels the same back but, understandably, could not hide his disappointment at failing to hang on for what would have been a truly spectacular end to 2016.
"The reaction is one you can imagine," Karanka said.
"I don't like to lose but I told them that apart from the result, the performance once again against a top team was really good.
"Again we competed against a top team. We will win games against teams around us. Once again we showed we are a consistent team and we had chances to score."