Mikel Arteta has already stressed repeatedly this season how important the entire squad is going to be if the Gunners want to take the next step under him, and this win over Everton underlined his point.
It had been six years since Arsenal had won here, back to the days when Arsene Wenger was in charge.
Their visits since then had been ones of disappointment and frustration, but finally their Goodison Park hoodoo is over.
For so long, it looked like it would carry on though as Everton turned this game into the scrappy affair they wanted. Arsenal had around 80 per cent possession in the first-half, but no penetration.
Their only real chance came via a goal that was ruled out for offside by VAR. Gabriel Martinelli’s joy was wiped out in seconds and moments later his game was over too, with injury forcing him off.
But when one door closes, another opens. Trossard was thrown on and he turned out to be Arsenal’s match-winner.
Before kick-off, it had felt like the talking point would be at the other end after Arteta dropped goalkeeper Aaron Ramsdale for David Raya.
Arteta made the point he had a deep squad, now competing in the Champions League, and rotation is inevitable. Everyone must play their part.
His words rung true, but not how he imagined it. Raya had a solid game, keeping a clean sheet, but it was Trossard who grabbed the headlines.
The Belgian took his goal brilliantly, too. Arsenal worked a short corner really well, with Bukayo Saka eventually picking out Trossard.
Taking it on the run, the winger guided the ball into the corner with his left foot and the ball kissed the post as it went past a diving Jordan Pickford.
Trossard was signed last January from Brighton for £26million and he has certainly out performed that price tag.
Ahead of a vital month for the Gunners, which sees them return to the Champions League, this was a crucial three points. Arsenal need to build momentum after a steady start and, with the games coming thick and fast every three or four days, everyone will get their chance.
Arteta will just hope that the rest of the squad follow Trossard’s lead.