Millwall travelled to Bell Lane on Saturday afternoon to face Mikel Arteta's Arsenal side in a pre-season friendly.
As The Lions continued their preparations for the 2021/22 campaign, Alex Mitchell scored the only goal for Gary Rowett's side as they were defeated by a strong Arsenal team.
New signing George Long was tested several times early doors as Arteta's side looked to break the deadlock, with Nicolas Pépé and Eddie Nketiah seeing their attempts denied.
As dangerous as the home side looked in the early stages, The Lions looked to counter and created two great chances to take the lead.
A free-kick awarded in the build up for Millwall was whipped in by Scott Malone and met by the head of Jake Cooper, who was only to be denied by the post.
Moments later and continuing to press in numbers, George Evans capitalised on a mistake by defender Pablo Mari.
Cutting the ball back to Tom Bradshaw, the strikers scuffed shot found Benik Afobe and his powerful effort from close range was well saved by Okonkwo.
It took a moment of magic from Arteta's side to break the deadlock. A stunning scissor-kick from Pierre-Emerick Aubameyang on the edge of the box smacked the crossbar, before Chambers headed in the rebound.
As the game entered the second-half, several changes came from both sides as the game began to open up with goals from Lacazette, Pepe and youngster Balogun, putting The Gunners into a comfortable position.
A special moment came for young Millwall defender Alex Mitchell in the dying minutes of the game.
The 19-year-old tapped home for The Lions after Danny McNamara's lofted ball in the box, was knocked down into a dangerous area by Murray Wallace.
The Lions' pre-season campaign continues next week, with trips to Gillingham and Ipswich Town awaiting Gary Rowett's side ahead of the 2021/22 season.
Millwall First-Half XI: Long; Romeo, Ballard, Pearce, Cooper, Malone, Evans, Leonard, Mahoney, Afobe, Bradshaw.
Millwall Second-Half XI: Long; Romeo (McNamara 60'), Ballard (Alex Mitchell 78'), Cooper, M.Wallace, Malone (Burey 77'), Thompson, Mitchell, Evans (Bennett 60'), Böðvarsson, Afobe (60')
Arsenal First-Half XI: Okonkwo, Chambers, Holding, Mari, Tierney, Elneny, Partey, Smith-Rowe, Pépé, Aubameyang, Nketiah
Arsenal First-Half XI: Hein, Chambers, Holding, Mari (Tavares 60'), Tierney (Cedric 60'), Partey (Willian 70'), Lokonga, Smith-Rowe (Maitland-Niles 70'), Pépé (Balogun 70'), Lacazette, Aubameyang (Nelson 70').