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...
I was surprise Manchester United won the game last night against Newcastle United, there win against Newcastle United has given them a chance to qualify for the conference league if Chelsea losses to Bournemouth which I doubt just as you, but football can funny and unpredictable anything can happen Bournemouth can shock the world by winning Chelsea puting Manchester United in a better position to qualify for the conference league.
this is just like an arsenal fan wishing that Man city will loose against Tottenham Hotspur so they will maintain their position on the top of the premier league table and then when it never happened they expect west Ham to win Manchester City in there next encounter. You can't expect others to loose before you succeed. Chelsea has gone back to her winning form and I don't see any form of loss in Thier last encounter against Bournemouth on Sunday. Chelsea even have an high chance of getting to the fifth position at the end of the day if Tottenham Hotspur isn't able to win shiefield UTD on Sunday but that's not even our concern. We're not moving anywhere below the sixth position and Manchester United will most likely remain in Thier 8th position.