A dominant first-half display was all the young side needed to seal a win against a French team who were poor defensively, with Nico Yennaris and Chuba Akpom grabbing the goals
The young English side were quick out of the blocks, scoring twice in the opening 20 minutes with Yennaris and Akpom the scorers. Akpom added a late third to seal a comfortable victory for the Gunners.
Arsenal almost got off to a great start playing down the considerable slope at Underhill, with Akpom chasing down a pass-back to Marseille keeper Ibrahima Sy, charging down the clearance, as it bobbled off to the wing in the first minute.
The Gunners went close again in the opening stages, when Kyle Ebecilio was slotted through, but when one-on-one with Sy, the keeper came out on top, pulling out a great stop.
And they didn't have to wait long for the opener, with Akpom showing nice feet to get in a cross on the left, which Yennaris converted from close range in the eighth minute.
Arsenal right-back Hector Bellerin was impressing as the Gunners cut through the Marseille defence with ease. The No.2 got down the line well, nutmegging opponents twice in the opening 20 minutes, before finding Akpom with a good cross that was headed over.
And in the 20th minute, the Gunners extended their lead when Serge Knabry raced onto a loose pass and found Akpom unmarked to poke home from close range.
Bellerin was again involved with Arsenal unrelenting in attack, this time he found Kristoffer Olsson, whose clever turn got him in behind the defence, but as Jon Toral converted from the cross he was adjudged offside.
The game took a surreal turn moments later, with Marseille keeper Sy coming out to clear a through ball, but rather than clear it he saw fit to take on an Arsenal player, before releasing it to a team-mate.
Bellerin almost made it three after 25 minutes, but after Martin Angha rounded the keeper and crossed, the right-back's shot was blocked on the line by Kevin Pommier.
The game was briefly paused while Yennaris received treatment following a clash of heads, and Marseille made two early changes, with Jean Batiste Massimi and Emanuel Loiacono replaced by Michel Araai and Stephane Sparagna after only half an hour. Oumar Diop was also substituted for Roukneddine Said Ali before half-time.
Marseille's only real attacking moment of the half came with the last kick, as Achille Anani hit a somewhat optimistic free-kick from 40 yards that cleared the crossbar by about 10 feet.
The Gunners started off the second half in a similar vein to the first attacking well with Olsson getting on the ball and dominating. His through ball to Yennaris eventually led to a shot on goal for Akpom, but it was a decent stop by Sy, who recovered well after it seemed he was beaten.
A bouncing ball through the Marseille defence caused panic as Sy again came rampaging off his line, but this time he was decidedly less composed, slicing an effort five yards to a team-mate, who hurriedly cleared.
Marseille made two more substitutions shortly into the second half, with Jonas Sommier and Jeremy Roland being replaced by Anthoine Kisaku and Gabriel Dubois, while Arsenal's first switch came with the impressive Toral going off for Anthony Jeffrey after 62 minutes.
A free-kick won after a great run from Angha was curled over by Ebecilio with 20 minutes to go, and though they looked more impressive in defence, Marseille weren't causing the Gunners any trouble in attack.
Gnabry, who had been impressive throughout, but particularly in the first half, left the pitch to a good ovation from the fans, being replaced by Alex Iwobi.
Marseille had a couple of chances to get in shots at Arsenal keeper Stuart Moore, but the stopper was ultimately untested, with Anani again blazing well over, this time from just outside the box.
And with under 10 minutes to go, Arsenal extended their lead, as Olsson slid in Akpom well for the striker to place a low effort into the far corner to seal a comfortable win.