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:
9. Miguel Almiron - 5
Largely anonymous before the break, though he did force a save from Ryan, taken off in the second half, never a threat in the opposition half Photo: Pool
10. Allan Saint-Maximin - 5
Forced a first-half save from Ryan with a dipping shot, but rarely got into his stride Photo: Stu Forster
11. Callum Wilson - 5
Handed his first start since February 6, tried to work the channels, but was well marked and all too often isolated upfront. Photo: Pool
12. Fabian Schar (for Fernandez, 72) - 4
Sent off on his comeback from long-term injury for a lunge, will be suspended for the next three games 4 Photo: Pool