Joe Smith Jr. stopped Bernard Hopkins 53 seconds into the eighth round of their WBC international light heavyweight title fight Saturday night.

Smith used a six-punch combination to send Hopkins through the ropes and on to the floor, effectively ending the 51-year-old's 28-year boxing career.

Smith successfully defended his title when Hopkins was unable to return to the ring after 20 seconds. Hopkins hit his head on the way down and twisted his right ankle — he cited the ankle as the reason he couldn't finish. A WBC official said the injuries incurred forced a TKO.

"I knew he was a true champion, and if he didn't get injured he'd be back here," Smith said. "I came here to do my job. This is my coming out party, too. I had to finish him. It was either my career was going to end and his was going to end, but I needed mine to continue."

Hopkins was reluctant to accept the outcome, initially claiming that he was shoved out of the ring.

"I was throwing the right hand and a combination and then using the rope as an offensive as I'm known for, and making a mess," Hopkins said. "He got frustrated, and I might have gotten glazed with a left hook and next thing I know he was throwing me out of the ring.

Smith sent Hopkins through the ropes and out of the ring to claim a TKO victory (Getty)

"The reason I said I'm upset they are giving Smith the TKO is because the momentum threw the ropes," he added. "I didn't dive through the ropes."

Hopkins (56-8-2) was looking to wrap his career with one last showing of defensive-minded boxing in front of an enthusiastic, star-studded crowd at the Forum. Instead, he finished in the same manor he started, with a loss.

"This is my last fight, I promised it would be and you come to that point in life where it is final and I'm happy with my retirement," Hopkins said. "I know the fans will know I went out as a soldier, fighting the toughest, baddest opponents. I'm not saying I agree, I'm not in denial — Joe was a tough, heavy hitting fighter."

Joe Smith Jr celebrates his victory over Bernard Hopkins on Saturday night (Getty)

Wearing his old Executioner shorts as a throwback to his earlier fighting days, Hopkins looked his age early as Smith (23-1, 19 KOs) was the aggressor to start. Hopkins regained some footing in the fifth and sixth rounds but Smith gained momentum and took it with him through the eighth, when he pummeled Hopkins in a corner and sent him through the ropes.

"I had seen him fall, and I kept hitting him until I saw him go out, and I landed that left hook until he went out," Smith said. "I knew he had time to go out, but I hit him with four or five clean shots and they were good shots on the button."

In his prime, Hopkins won a record 20 consecutive middleweight title fights. He became the oldest-ever champion when he defended his light-heavyweight belt at 49. However, Hopkins hadn't fought in more than two years, losing to Sergey Kovalev on Nov. 8, 2014, in his last bout.

Hopkins retired after 28 years in the ring (Getty)

Oleksandr Usyk (11-0), a 2016 Olympic heavyweight gold medalist out of Ukraine, successfully defended his WBO cruiserweight title with a knockout of Thabiso Mchunu (17-3) with a knockout in the ninth round, his 10th.

Local El Monte product Joseph Diaz (23-0), wearing Lakers colors in their former home, defended his NABF featherweight title, beating Horacio Garcia (30-2-1) of Mexico in the NABF featherweight title by unanimous decision.