I can't say Man U played better than Newcastle, but I guess the home field factor played a major role... They were lucky in this match and to be honest their game was much better than the previous ones... Now Newcastle and Devils have the same number of points in the standings and there is a small chance to get into the Conference League if Chelsea lose to Bournemouth, which I doubt...
Now it's reversed and Chelsea are better than Manchester United or Newcastle. 
But it's true that last night's game played an important role for them playing at Old Trafford at least it was confidence especially by playing some of their academy players who performed quite well while Rashford and Hojlund were inserted at the end although at the end there was a contribution for them.
Remember that I'm back to doubting again for week 38 with Brighton so until now Manchester United still can't be consistent and this is also the last match.
As I understand it, Chelsea will remain ahead of United regardless of the results of the last round - thanks to a better goal difference. As for Newcastle, United need to beat Brighton and hope that Newcastle loses points (since they also have a much better goal difference), but given that United plays Brighton and Newcastle plays Brentford, I rather expect United to lose points.
If no surprises happen, United will remain in 8th (lol) place.