The striker produced a stunning display in front of goal as Arsene Wenger's men coasted to victory
The Frenchman - used sparingly by Arsene Wenger last term - scored a first-half hat-trick and added a fourth to his personal haul after the break at the Emirates Stadium as Alexis made his bow.
Sanogo opened the scoring 26 minutes in against the Portuguese champions when Aaron Ramsey crossed for the Frenchman to backheel into an empty net.
If the half began at a relatively slow pace, the finale was quite the opposite as Joel Campbell - returning from a loan spell at Olympiacos - volleyed home from inside the area after 40 minutes.
Sanogo then wrapped up his hat-trick as first he tapped home Campbell's pass and then nudged an effort past Artur Moraes for the fourth.
The former Auxerre man's lethal finishing continued after the break as he quickly added Arsenal's fifth.
Nico Gaitan pulled one back with a header shortly after the hour but it mattered little, with home fans treated to a convincing showing as well as first glimpses of recent signings Alexis and Calum Chambers.
Arsenal began the brighter and pressed Benfica well, with the returning Campbell among those to catch the eye.
Chambers was deployed in the centre of defence alongside Nacho Monreal and the pair were left watching when Gaitan struck the crossbar from Maxi Pereira's cutback 10 minutes in.
Sanogo was almost able to divert Tomas Rosicky's wayward shot home soon after as Arsenal's front four continued to create openings, albeit initially lacking the required sharpness in front of goal.
Benfica saw recent acquisition Eliseu limp off with 19 minutes gone before Monreal almost steered the ball past Damian Martinez.
However, Sanogo opened the scoring shortly after - Ramsey losing his marker with a clever touch before adeptly turning the ball over the line.
With Arsenal in full flow, Campbell volleyed home the second from Rosicky's delivery before Sanogo added two more to send Wenger's men in comfortably ahead.
It took just four minutes of the second half for Sanogo to strike again as he followed up up Ramsey's saved shot to tap home from 10 yards.
Both sides made a host of changes before the hour mark, with Wenger forced to withdraw Campbell, who appeared to pick up a knock.
After the flurry of substitutions, Arsenal were caught cold as Gaitan headed home from Pereira's long throw.
Alexis joined Chambers in making maiden Arsenal appearance to cap a fine day for the home side, who were denied another goal late on as both Ignasi Miquel and Francis Coquelin struck the woodwork.
Arsenal meet Monaco on Sunday, one week before the FA Cup winners' Community Shield clash with Manchester City.