The finish came 1:44 into the third frame, when Overeem (42-15) landed a perfect knee under Hunt's chin along the fence. The shot immediately put Hunt (12-11-1) down for good.
It's a nice rebound for Overeem, who suffered a first-round knockout loss to Stipe Miocic in a title fight in Cleveland.
It actually marks his second career victory over Hunt. The two met in July 2008 under the Dream banner. Overeem won that fight via submission.
"This man is tough, I've fought him once before," Overeem said. "I'm actually a fan of Mark. He's showed tremendous skill throughout his career."
One of the most significant blows of the fight was actually a checked kick by Overeem. Hunt's right shin bled badly after Overeem blocked an early leg kick, although it didn't stop Hunt from throwing it later in the fight.
Hunt wobbled Overeem on several occasions, but was unable to finish him off. He staggered him with a right hand in the first and then an elbow in the second. The New Zealander appeared to run out of gas late, however, which allowed Overeem to control him along the fence.
Overeem, of the Netherlands, has now won five of his past six bouts. The 36-year-old will likely need at least one more victory to get back into a title fight, but he's not far off.
At the post-fight press conference, UFC president Dana White revealed Overeem dealt with food poisoning leading up to the fight.
"He's been in the hospital the last 24 hours with food poisoning," White said. "Throwing up and all the other pleasantries that go with food poisoning. He was in the hospital, we brought him back and then had to take him back to the hospital.
"He did not want to turn down the fight and still came out and knocked out Mark Hunt. And more to his credit, he didn't say it in his [post-fight] interview."
Teymur upsets Vannata in dramatic fashion
Swedish lightweight David Teymur (6-1) certainly made the most of a co-main event spotlight.
In a major upset, Teymur defeated Lando Vannata (9-2) via decision. All three judges scored every round for Teymur, resulting in unanimous 30-27 scores.
The 155-pound fight was much closer than the scores looked, however. According to Fightmetric, Vannata barely trailed Teymur in total strikes landed. Teymur landed 73 compared to Vannata's 66.
But the harder shots did seem to come from Teymur. The southpaw landed heavy left hands in the pocket and snapped Vannata's head back in the second round with a thunderous Superman punch. The inside leg kick also landed for Teymur and although he wasn't able to hold Vannata down, he added takedowns at key moments.
Fighting out of Jackson-Wink MMA in Albuquerque, New Mexico, Vannata brought his usual style points to the matchup. At one point, he caught a body kick attempt from Teymur and launched into a spinning back kick of his own. He also dropped Teymur in the opening round with a punch, but Teymur popped right back up.
A former contestant on The Ultimate Fighter, Teymur is now 3-0 in the UFC.
Kelly ruins Evans' middleweight debut
Surprising middleweight Dan Kelly (13-1) continues to impress at age 39, as he earned the biggest win of his career against former light heavyweight champion Rashad Evans.
Kelly, 39, won the fight via split decision (29-28, 29-28, 28-29). ESPN.com scored it for Kelly, 29-28. It was Evans' middleweight debut.
The left hand was a big weapon for Kelly. He appeared to hurt Evans briefly in the second round with an uppercut and looping cross.
Evans (19-6-1) struggled to find his range early and was ineffective with his grappling. He pushed the pace in the final round and landed a handful of clean punches, but Kelly was never in trouble. It marks Evans' third loss in a row. He exited the Octagon immediately following the loss.
For Kelly, who fights out of Melbourne, Australia, it is his sixth win inside the Octagon. He has suffered only one defeat, a TKO loss to Sam Alvey in 2015.
Elkins, nearly out, pulls off major comeback
A 5-to-1 betting underdog, Elkins looked completely out of his league early in the fight. Bektic peppered him with right hands and dropped elbows onto his face after powering through a takedown.
Despite suffering multiple facial cuts, Elkins battled back in the third. The Team Alpha Male product landed a big right hand to the chin after Bektic turned his back and then finished the fight with a big head kick.
Elkins has now won four in a row and 12 in the Octagon overall.