In 2002 Los Angeles, a young Adonis "Donnie" Creed sneaks out with his best friend, Golden Gloves champion Damian "Diamond Dame" Anderson, to watch Dame compete in an underground boxing match. After Dame's victory, Dame tells Donnie about his aspirations to turn professional and become a world champion. During a detour at a liquor store, Donnie impulsively attacks a man named Leon.Fifteen later, in 2018 Donnie fights and wins in a rematch against "Pretty" Ricky Conlan, who just got released from his prison sentence and worked his way back to be a contender for championship fight. He retires from boxing to focus on his wife Bianca and their daughter Amara. Three years later, Donnie runs Delphi Boxing Academy with his coach Tony "Little Duke" Evers Jr., and is promoting his protégé, world champion Felix "El Guerrero" Chavez, in a match against Viktor Drago. Due to her hearing problems, Bianca forgoes performing and becomes a successful producer. The two keep watch over the declining health of Donnie's adoptive mother Mary Anne. Amara aspires to be a boxer like her father, which gets her into trouble in school.Dame is released from prison and reconnects with Donnie, to whom he shares his desires to continue his boxing career. Donnie reluctantly invites Dame to the gym to spar with Chavez, however his aggressive style draws scorn from Chavez and Duke. Dame later visits Donnie's home, where he meets his family and shares about their time together at a group home, which Bianca has never heard of. Privately, Dame expresses his desire for a title shot against Chavez, citing Donnie's previous one-in-a-million shot, which Donnie refuses.At a party for Bianca's record label, Dame cryptically tells Bianca about Leon before Drago is attacked by an unknown assailant; his injury casts doubt on his fight with Chavez. Donnie suggests Dame as an opponent, pitching an underdog fight much like how his father gave Rocky a first title shot, which Chavez gladly accepts. During the fight, Dame fights dirty, but knocks out Chavez, winning the undisputed heavyweight championship.After the match, an uneasy Donnie visits Mary Anne, who shows him letters Dame wrote to Donnie while in prison that she kept from him due to believing he was a bad influence. One letter contains a picture showing Dame with a fellow inmate that Donnie recognizes as the one who assaulted Drago. Realizing Dame orchestrated the attack, Donnie confronts him. Dame reveals that he manipulated all their encounters to set him up as a champion to enact revenge for Donnie abandoning him during his arrest and jail time, before giving him a black eye. Donnie is unable to open up to Bianca about his guilt over Dame, who revels in his newfound fame and publicly slanders Donnie as a fraud who turned his back on him.Mary Anne suffers another stroke and dies. After the funeral, Donnie confesses to Bianca the truth: Leon was the abusive caregiver in the group home Dame and Donnie lived in before Donnie was adopted. After Donnie attacked Leon at the liquor store, a brawl against Leon's friends ensued causing Dame to pull a gun. As cops arrived, Donnie fled, but Dame was arrested. Attempting to block out the memory, Donnie never contacted Dame out of shame and guilt. Knowing Dame would not stop defaming him, he tells Bianca there's only one way to bring him down.Donnie goes on First Take, where Dame calls in to goad Donnie over the phone. Donnie decides to come out of retirement and challenges Dame for the championship, which he accepts. After training with Duke and a recovered Drago, Donnie faces Dame in the "Battle of Los Angeles" at Dodger Stadium. Donnie faces Dame in a grueling, evenly matched affair. In the final round, Donnie uses Duke's advice to let go of his fear and guilt and takes advantage of Dame's drained energy, delivering a knockout to win the match and the championship. Afterwards, Donnie reconciles with Dame, with both men admitting it was not the other's fault. Donnie joins Bianca and Amara in the ring in the empty stadium, where he pretends to box with Amara.