Rosenior had rather ironically insisted Arsenal were far more than a team who relied on set-pieces, before the Gunners struck early from a dead-ball situation.
It was a goal of alarming simplicity to concede for the Blues, with Robert Sanchez caught in no man’s land when Ben White headed home from Declan Rice’s delivery for his first goal since netting a brace against the Blues in April 2024.
Nevertheless, Chelsea’s response was encouraging.
They worked a promising opening when Enzo Fernandez threaded a pass towards João Pedro, but the Brazilian dragged his effort wide. Estevao then tried his luck following a darting run down the right-hand side before being denied by Kepa Arrizabalaga at his near post.
The hosts’ defensive vulnerabilities were clearly evident, though, and William Saliba wasn’t far away from doubling Arsenal’s advantage when his long-range shot grazed the roof of the net, in what had been an intriguing first half.
It took a mere five minutes into the second half for Mikel Arteta’s men to double their advantage, in another goal which hardly left Sanchez covered in glory.
Bukayo Saka fed in White down the right, and the latter’s cross slipped the Spaniard’s grasp before Viktor Gyokeres slid the ball home.
Rosenior brought Alejandro Garnacho on from the bench in response, and the Argentine halved the deficit within four minutes of his introduction after clinically dispatching his strike at the far post from Pedro Neto’s cross.
But just when Chelsea were contemplating a comeback on the night, the Gunners delivered what could be a potentially fatal third goal.
There was nothing scrappy or fortuitous about this one, as Gyokeres deftly teed up Martin Zubimendi to twinkletoe his way through Chelsea’s defence before unleashing an unstoppable left-footed strike past Sánchez.
The Blues' shot-stopper was enduring a rough night, but he partly redeemed himself with a superb save to keep out Mikel Merino’s shot.
Arsenal would have been expected to see out the game comfortably from that point, but Garnacho struck again to inject more jeopardy into this two-legged tie.
Neto was the architect once more, as his corner was cleared into his path to fire a left-footed shot which took a bounce before beating Kepa.
Chelsea ultimately couldn’t manage a full-scale comeback, yet despite the defeat, Rosenior would have been pleased by the determination his young side showed against this impressive Arsenal team.
Meanwhile, this will feel like somewhat of a missed opportunity for the Gunners, and Arteta will believe this tie is far from over ahead of the second leg.
Flashscore Man of the Match: Martin Zubimendi (Arsenal)