Steve Bruce reflected on a "horrible 20 minutes" after his Newcastle United side crumbled at Old Trafford.
The Magpies went down 4-1 but threw the game away after taking an early lead through Matty Longstaff.
Bruce's side have a quick turnaround with Everton coming up next at St James' Park.
But after the defeat in the North-West, Bruce said: "We have had a horrible 20 minutes before half-time and just after half-time where we have made too many mistakes.
"When you come here the one thing you can't do is gift Manchester United.
"I know it's Christmas but we gave away more goals in half an hour than we have in three months. "It's a harsh lesson for us that you cannot make the mistakes we have just made."
Bruce spoke about the game drifting away from his side.
He added:"They have quality at the top end of the pitch but I thought for half an hour we were good. We gifted them a goal to start with.
"All of a sudden the game is away from you.
"If you chase it they will rip you to bits.
"We stuck at it but it was a tough afternoon for us."
