After netting from 30 yards against Hull on Saturday, the Swiss midfielder did it again after 23 minutes as the Gunners took firm charge at the City Ground.
Lucas Perez’s first two goals for Arsenal put Arsene Wenger’s side well in control in the second half – moments after a fan was led away for offering the Frenchman food.
The goalscorers, who cost a combined £47m this summer, ensured Wenger’s 11 changes from the 4-1 win at Hull were rewarded as ex-Gunner Nicklas Bendtner had a tough full debut for the hosts.
The sides traded early shots with Pajtim Kasami firing just wide for Forest before Jeff Reine-Adelaide blasted over for Arsenal on his debut.
Then Bendtner pounced on some sloppy defending and set up a glorious chance for Kasami with a clever cross but the midfielder shot wide.