Steve Bruce’s side fell behind on five minutes when Mohamed Elneny scored his first-ever top-flight goal.
Pierre-Emerick Aubameyang then continued his goalscoring run against the Magpies as the Gunners cruised to victory.
United remain nine points above the relegation zone ahead of the final four fixtures.
Our reporter Miles Starforth was at St James’s Park – and here’s how he rated each Newcastle player on a disappointing afternoon:
1. Martin Dubravka - 6
Pulled off a superb first-half save to deny Xhaka, kept busy by a dominant Arsenal team
Photo: PETER POWELL
2. Jacob Murphy - 5
Gave the ball away too often, and never really got on the front foot.
Photo: RICHARD SELLERS
3. Federico Fernandez - 5
Replaced by Schar in the second half, was on a yellow card.
Photo: Alex Pantling
4. Ciaran Clark - 5
Anchored a five-man defence, put in a committed performance
Photo: ALEX PANTLING