Man Utd find their groove Matty Longstaff struck the winner for Newcastle over Manchester United in October – a real low in Ole Gunnar Solskjaer’s side’s erratic start to the season. At one stage on Boxing Day it looked as though the 19-year-old was going to deal the Manchester United boss another major hit with just his second goal as a pro.But – with some help from Longstaff’s team-mates – Manchester United found a foothold and then hammered home their advantage quickly, with a swagger that made you wonder whether these really were the same players who crumpled to the embarrassing defeat at Watford four days ago. Man United 4-1 Newcastle – Match report and highlightsFind out more about Sky SportsPremier League Table | FixturesNewcastle ‘keeper Martin Dubravka should have done better with Anthony Martial’s powerful equaliser but he could do nothing about Mason Greenwood’s crashing drive, which picked up a feint deflection on the way through but still underlined the 18-year-old as a rising star.Marcus Rashford then took his season’s goal tally to a career-best 11 league goals with an uncharacteristic towering header before Martial profited from Sean Longstaff’s woeful back pass to finish clinically barely five minutes after…