Arsenal remain in sixth place, but are now eight points off the top four and Champions League qualification.
"I felt defensively we were very poor and made big mistakes," manager Arsene Wenger said. "I believe we were not good enough, I believe we were not disciplined enough."
Liverpool tightened their hold on a top-four place with a 3-0 win at Huddersfield. Emre Can, Roberto Firmino and Mohamed Salah scored as the Reds rebounded from consecutive losses to Swansea in the league and West Brom in the FA Cup.
"It was exactly what we needed," manager Juergen Klopp said. "It was nearly perfect — not the performance, the result."
Klopp's team is now five clear of fifth-placed Tottenham.
Elsewhere, West Ham and Crystal Palace each moved up in the table after drawing 1-1.
West Ham climbed up to 10th, with Palace now 12th.
- AP