Saka was however forced off with a suspected ankle injury on the half hour mark and was replaced by Reiss Nelson.
Saka’s injury stalled Arsenal’s momentum initially but they were rampant after the break as Nelson found the net twice.
Nottingham no Forest’s coach Steve Cooper made two attacking subs, bringing on Bradley Johnson and Emmanuel Dennis, but the one-way traffic continued with Nelson teeing up the impressive Thomas Partey who rifled a first-time shot from distance in the top corner to make it 4-0.
Martin Odegaard added Arsenal’s fifth after dispatching a powerful finish from Gabriel Jesus’ lay-off.
Arsenal are now two points clear of second place Manchester City