The striker produced a stunning display in front of goal as Arsene Wenger's men coasted to victory
Manager Arsene Wenger saw his Arsenal side take the lead through Sanogo just before the half-hour mark after edging the early stages. He picked up a pass from Aaron Ramsey and tapped in from close range.
But a flurry of goals then came either side of the interval. First, Joel Campbell doubled his side's lead with a fine half-volley, before setting up Sanogo for his second and Arsenal's third.
And 21-year-old Sanogo completed his first-half hat trick right on halftime, floating the ball over Artur Moraes in the Benfica goal to give his side a comfortable lead as it headed into the break.
Immediately after the restart, Arsenal had scored again. It was Sanogo once more who capitalized on a fine free-flowing move from the Gunners, firing in a rebounded effort from Ramsey's initial shot.
Attacking midfielder Nicolás Gaitan then pulled one back for the visitors just after the hour mark after poking the ball into the net from a header, just before new arrival Alexis Sanchez came on for the latter stages to make his Arsenal debut.