- Miguel Almirón (29')
- Lewis Hall (36')
- Joe Willock (61')
Manchester United manager Erik ten Hag looked shocked on the sidelines as his team were booed off the pitch, with the Dutchman under intense pressure following their 3-0 home defeat by Manchester City on Sunday.
"We know it is not good enough," Ten Hag told Sky Sports. "We have to take responsibility for it, I have to take responsibility for it. We don't give the performance, I feel sorry for the fans."
In a repeat of this year's final at Wembley, which Manchester United won 2-0, Newcastle led 2-0 at half-time thanks to goals by Miguel Almiron and Lewis Hall before extending their lead through Joe Willock to ease into the quarter-finals.
Newcastle took the lead when Almiron scored in the 28th minute after Tino Livramento won the ball and set up the Paraguayan to slot the ball past keeper Andre Onana with a sliding finish.
Hall doubled the lead eight minutes later, volleying into the far corner after a poor clearance and the misery continued for the home crowd when Willock sliced through the defence and slotted his shot into the bottom corner around the hour mark.
"I think the spirit of the group just showed in the performance, the togetherness, the unity," Magpies manager Eddie Howe said.
"This is a really tough place to come and to score the goals we did at the times we did and just the manner of the performance really pleased me."
Manchester United have lost eight of their last 15 games in all competitions -- their worst run since 1972.
- Robert Jones