Lesnar had been finished by a 6-foot-5 Dutch kick boxer in the first round at UFC 141. A few minutes later, the UFC's former heavyweight champion finished his own meteoric mixed martial arts career.
Lesnar retired from the UFC after Overeem stopped him with one vicious kick to the body at 2:26 of the first round in their heavyweight bout Friday night, leaving the UFC heading into 2012 without its biggest pay-per-view star.
"This is the last time you'll see me in the octagon," Lesnar said.
Largely thanks to his fame from a career in pro wrestling, the hulking Lesnar (5-3) played a significant role in expanding the UFC's profile and fan base over the past four years. He beat Randy Couture in 2008 to win the heavyweight title, defending it twice before losing the belt to Cain Velasquez last year.
But Lesnar has fought just three times in the past 2½ years while dealing with bouts of a lower-intestinal ailment that nearly killed him. The accumulation of pain and rehabilitation finally undid Lesnar, whose famed strength and stubbornness couldn't overcome diverticulitis.
"I've had a really difficult couple of years with my disease, and I'm going to officially say tonight is the last time," Lesnar said.
Lesnar's return from a 14-month injury absence was a short, one-sided beating. After taking damage from two knee blows early on, he couldn't recover from a kick to the liver from Overeem (36-11), who made a stellar UFC debut despite getting cut near his right eye by a punch from Lesnar.
The 34-year-old Lesnar's announcement stunned fans who already realized he faced a difficult matchup in the UFC's traditional end-of-the-year event in its hometown. The matchup was a classic MMA clash of styles, with Lesnar's brute wrestling contrasting sharply with Overeem's vicious striking.
"I had no idea he would do that, (but) am I surprised? No," UFC President Dana White said. "Brock Lesnar has made a lot of money in his career and has achieved a lot of things. ... He brought a lot of excitement to the heavyweight division. What he accomplished in a short amount of time is amazing, but I get it. It doesn't shock me."
Overeem is three years younger but much more experienced than Lesnar, hurting the former champion at least twice earlier in the round while Lesnar failed in his attempt at a one-legged takedown.
"I promised my wife and my kids if I won this fight, I would get a title shot, and that would be my last fight," Lesnar said. "But if I lost tonight ... you've been great."
Overeem will get the next shot at UFC heavyweight champion Junior Dos Santos, who watched from a seat near the octagon.
Overeem is a champion kick boxer who has fought in multiple promotions over the past decade, winning titles in Dream and Strikeforce with nearly unbeatable striking and size. He joined the UFC in September, finally presenting his formidable skills and intimidating physique to the sport's largest audience.
"My experience in UFC was, it's huge," Overeem said. "I think it's like 100 times bigger than Strikeforce. K-1 (kick boxing) is big, but this is a lot bigger. I was a little bit blown away, still am. I loved every second of it."
White might have given an immediate title shot to Overeem if the timing had been better, but Dos Santos only claimed Velasquez's belt in early November. Overeem welcomed a debut against Lesnar, even guaranteeing a knockout in the first two rounds.
"First or second round, I promised," Overeem said.
Lesnar hadn't fought since losing his heavyweight belt to Velasquez in October 2010, cancelling a bout against Dos Santos last June in Vancouver after another flare-up of diverticulitis. The former NCAA wrestling champion and fake WWE wrestler kept his unparalleled popularity during his recovery, and Lesnar used the time off to modify both his diet and his standup game, attempting to improve his biggest weakness.
As it turned out, Lesnar couldn't improve enough to contend with the supremely skilled Overeem, who embraced Lesnar afterward.
The undercard at the MGM Grand Garden featured two upsets: Lightweight Nate Diaz won a bloody unanimous decision over Donald "Cowboy" Cerrone with superior boxing, and Johny Hendricks stopped welterweight star Jon Fitch with one punch just 12 seconds into their bout.
In the co-main event, Diaz (15-7) backed up his tough talk and rude behavior in a fight that had the sellout crowd on its feet as he battered Cerrone, nearly a 3-to-1 favorite in the MGM Grand sportsbook, for most of the three-round standup fight.
Diaz, the brother of bad-boy welterweight Nick Diaz, picked apart Cerrone's defense for most of the fight, leaving Cerrone bloody after his first loss in seven fights since September 2010.
Cerrone (17-4) knocked down Diaz at least a half-dozen times with kicks and leg-whips, but Cerrone refused to fight Diaz on the ground, repeatedly allowing Diaz to get up.
The unusual strategy showed respect for Diaz's ground skills, but also minimized the importance of those knockdown shots in the eyes of the judges, who scored the bout 30-27 twice and 29-28 once, all for Diaz.
Hendricks (12-1) ascended to elite status with one sneaky left hook that caught Fitch (27-4-1) right on the button, flattening the favored San Jose fighter, whose return from a 10-month absence was stunningly brief. Hendricks, a two-time NCAA champion wrestler at Oklahoma State, completely stunned Fitch, who had lost just one fight since December 2002.
Unbeaten featherweight Jim Hettes got new fans' attention with a comprehensive thrashing of veteran Nam Phan, repeatedly threatening to finish the fight with strikes and ground work.