Jose Mourinho's side had chances to equalise but could not find a way past a committed Newcastle team that gave their survival hopes a big boost by claiming all three points.
Some late United pressure ensued, and Dubravka made an fantastic last-gasp save to cement hero status for a fine debut, and the defiant hosts held on for what is arguably their most important victory of the season.
The Englishman lined up in a front four containing Alexis Sanchez, Romelu Lukaku and Anthony Martial, but was easily the worst of the quartet going forward. A Dwight Gayle free-kick was deflected into the path of Jonjo Shelvey, who stung the palms of David De Dea from the edge of the box.
A huge chance fell the way of the Frenchman in the 35th minute when he was played through on goal by Nemanja Matic.
"There are so many awards - performance of the week, manager of the month and this and that - they should give one (to) the guy that behaves best on the touchline and it should be the fourth official to vote". Referee Craig Pawson was close enough to see the incident, booking the defender for a dive.
From the resulting set piece, Florian Lejeune was allowed to rise unchallenged at the far post and Ritchie swept home as United stood watching in the centre of the goalmouth. Michael Carrick came on for Pogba, at the same time that Jesse Lingard replaced Juan Mata, and Mourinho has explained that he made the change in order to tweak his formation, though it had little effect.
"They fought for their point, a point is what they had in mind", continued Mourinho, who astoundingly still hasn't won at St. James Park.
United will have to quickly put the result behind them though if they wish to remain in the Champions League spots otherwise their season will quickly unravel.