Hopkins, a month shy of his 52nd birthday and participating in the 67th and final fight of a career that began when Ronald Reagan was president and the year before Smith was born, landed on his head but complained of an ankle injury and was unable to continue.
Referee Jack Reiss administered a 20-count, as is the boxing rule when a fighter is ejected from the ring. When Hopkins could not get back into the ring in time, Reiss waved off the light heavyweight fight at 53 seconds, to the disappointment of most of the 6,513 who turned out to see whether Hopkins could go out with a win in his first fight in 25 months. On Nov. 8, 2014, the date of Hopkins' prior fight, he lost two light heavyweight world titles to Sergey Kovalev in a one-sided decision in a unification fight.
While the result was a career-making victory for Smith, Hopkins' hand-picked opponent for his career finale, it was an ignominious ending for one of the greatest fighters in boxing history. Hopkins was the undisputed middleweight champion. He made a division-record 20 title defenses, was a three-time light heavyweight titleholder and set several age-related records, including becoming the oldest fighter to win a world title, first at age 46 and then again at 48.
Those are stats that will be remembered when Hopkins (55-8-2, 2 no contests, 32 KOs) goes into the International Boxing Hall of Fame, but the wild ending of this fight won't soon be forgotten.
In the eighth round, Smith caught Hopkins along the ropes with a six-punch combination, including a finishing left hand that caught Hopkins as he was bending over. Hopkins fell between the ropes and crashed to the arena floor.
"I was throwing the right hand and a combination and then using the rope 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.
"I injured myself and hit my head first and hurt my ankle. I knew of the 20 seconds, but couldn't stand up on my feet because my ankle was injured. I said I could walk but I couldn't box. I had a choice to make, but I guess the referee made it for me. I know if I hadn't made a mess and gotten knocked out of the ring, I would've come back like I'm known for and would've had my chin."
The ending was somewhat reminiscent of a middleweight title defense Hopkins made against Robert Allen in Las Vegas in 1998, when he was accidentally pushed out of the ring in the fourth round by referee Mills Lane as he tried to break the fighters. Hopkins suffered an ankle injury, and the fight was declared a no contest.
"I knew he was a true champion, and if he didn't get injured, he'd be back here," Smith said.
There were several minutes of uncertainty in the eighth as nobody seemed to know whether the fight was over, even though Reiss had counted to 20 in the ring.
"The fighter got hit with a legal punch and went out of the ring and injured himself on the way out," Reiss said. "He wasn't going to continue. I counted to 20, and he couldn't continue, so the fight is over."
At the time of the stoppage, Smith was ahead 69-64 and 67-66 on two scorecards, and Hopkins was up 67-66 on the third card. ESPN.com had Smith ahead 67-66.
"This was the round I was going to make something happen," Hopkins said of the eighth round.
When the fight was made, Hopkins announced it would be his last one -- win, lose or draw -- and he stuck to that after the fight.
"The reason I said I'm upset they are giving Smith the TKO is because the momentum threw me throughthe ropes," Hopkins said. "I didn't dive through the ropes. 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. 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."
Hopkins came back because he wanted to finish his career on his own terms, and while the fight might not have ended how he wanted, he put in a good effort before the wacky ending.
Smith got off to a solid start, out-landing Hopkins 14-4 in the first round and maybe surprising Hopkins with his power as he backed him up.
In the early going, Hopkins seemed to be trying to shake off the long layoff. His timing looked off, and his legs were a bit shaky as Smith went after him and landed a left to the body that stood up Hopkins in the second round. But Hopkins responded with a right hand and also opened a cut over Smith's left eye on a head butt that did not look accidental.
Hopkins has guile and experience, but he can't go three hard minutes per round anymore. However, he fought in spurts and also landed some powerful right hands, especially in the fifth round, in which they both connected.
Smith, who earned $140,000 to Hopkins' $800,000, continually marched forward firing punches, while Hopkins would throw a right hand and then lunge to tie him up. But in the eighth round, Smith caught Hopkins along the ropes and fired the fight-ending combination.
While Hopkins was disappointed with the way the fight ended, Smith (23-1, 19 KOs), a 27-year-old union laborer from Mastic, New York, was happy to get the biggest win of his career and a second upset in a row. He had gained Hopkins' attention with his upset, first-round knockout of contender Andrzej Fonfara in June, and months later, earned Hopkins' pick for his final fight.
"It feels great, it's the best feeling in the world to accomplish something I set out for and wanted to do," Smith said. "I had seen him every time I threw the right hand. He was throwing the left. I had seen him fall, and I kept hitting him until I saw him go out [of the ring], and I landed that left hook until he went out.
"I hit him with four or five clean shots, and they were good shots on the button. 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. I'm going to get back in the gym and train hard for my next opponent. I'm up for anything."
As he prepares for retirement, Hopkins says he'll promote in his role as a partner in Golden Boy Promotions, and enjoy the fruits of his labor, his family and the millions he has earned.
He can also look back on a career in which he pulled memorable upsets against Felix Trinidad, Antonio Tarver, Kelly Pavlik and Jean Pascal -- not to mention knocking out Oscar De La Hoya and becoming the first fighter in any division in the four-belt era to hold all of them at the same time.
"Things unfortunately happen," Hopkins said. "I don't want the fight to end the way it did. I'd rather get beat or a win where it's clear to everybody. But I'll say it one last time. I'm really serious about this: Win, lose or draw -- trust me, if it had been the other way around -- win, lose or draw, or controversy, that's it.
"I have no regrets."