The Swede’s 12th-minute header came after the Gunners failed to clear their lines and Anthony Gordon sent a sumptuous ball into the area.
Arsenal had started the game well but once Isak found the net they struggled to get a handle on proceedings and lacked creativity in the final third.
Mikel Arteta made changes in the second half to try to break down Newcastle’s resolute defence but his side registered just one shot on target across the 90 minutes.
Victory for the Magpies moves them up to eighth in the league while Arsenal are third and will find themselves eight points adrift of Manchester City in top spot should Pep Guardiola’s side beat Bournemouth later on Saturday.
