Check out the clip, the boys positioned his casket so they could redirect a soccer ball off of it ... and when the ball slid past the keeper into the makeshift goal -- things got emotional.
All of his teammates surrounded the casket, hugged it and sobbed uncontrollably.
Sports reporter Guillermo Schutz posted the vid to social media ... captioning it in Spanish, "In Oaxaca, this is how they bid Alexander a final goodbye, the 16-year-old teen murdered by municipal police. His friends honor him with one last goal. We're all crying."
The footage was so touching ... even former UCLA hoops star Lorenzo Mata had to share it on Twitter.