Alexis Sanchez looked guaranteed to score after rounding Newcastle goalkeeper Martin Dubravka, but his hesitation came back to bite Manchester United on a tough afternoon in the north east.
Just minutes later, Matt Ritchie popped up to score the only goal of the game, securing Newcastle a much-needed three points in their fight against relegation.
United, meanwhile, stay second but missed the chance to extend their gap on the other Champions League -chasing teams below them.
More to follow.
Matt Ritchie wheels away in celebration after arriving in the box to fire the ball past David de Dea and give Newcastle the lead Ritchie looked delighted as he sprinted to the corner flag before sliding on his knees in front of the adoring Newcastle fans The home side were desperate for points in their relegation battle, and Ritchie's first goal of the season was hugely important Chris Smalling sums up the feelings of Manchester United players and fans as he watches on following Newcastle's opener Dwight Gayle may feel aggrieved not to have been awarded a penalty before half-time after being brought down in the box Gayle fell outside the box under Smalling's challenge, but referee Craig Pawson opted to give neither a free-kick nor a penalty Rafa Benitez was incensed with the decision to wave away Newcastle's penalty claims, arguing with the fourth official Martin Dubravka endeared himself to the Newcastle fans on his debut when he saved from Anthony Martial's one-on-one Martial lies on the St James' Park turf, frustrated after missing a gilt-edged chance to put United ahead in the first half Alexis Sanchez, the Premier League's highest-paid player, was once again included in Manchester United's starting XI Jesse Lingard fires a shot towards the Newcastle goal, past the body of Jamaal Lascelles, but cannot find the back of the net Manchester United boss Jose Mourinho, pictured trying - and failing - to catch the ball, has never won at St James' Park One player that did successfully catch the ball was Dubravka, who replaced Karl Darlow in the Magpies' starting line-up Dubravka was hugely impressive on his first outing, regularly saving and dominating his penalty area at St James' Park Romelu Lukaku heads the ball into the back of the Newcastle net, but it is disallowed due to a push in the build-up Sanchez missed a number of huge chances to put United ahead before Newcastle's eventual opening goal on Sunday Sanchez falls on the ball after tangling with Newcastle midfielder Ritchie during a hard-fought contest in the north east Gayle grits his teeth after missing a chance to get in on the act, but he later turned provider to set up Newcastle's goal Ritchie picks up a pass from striker Gayle to slide the ball into the bottom right-hand corner of the Manchester United net The former Bournemouth man's first goal of the season couldn't have arrived at a better time for him and his team-mates Ritchie's team-mates were quick to join the scorer in riotous celebrations at St James' Park on a hugely important afternoon Mourinho's disappointing record at St James' Park goes on - the United boss has now not won there in seven league games