Overeem (45-17) finished Oleinik (57-12-1) via TKO at the 4:45 mark of the heavyweight bout. He hurt Oleinik badly with standing knees before stopping him with additional strikes on the ground.
Overeem, 38, was originally scheduled to face Alexander Volkov (30-7), but Volkov withdrew due to injury. Overeem expressed interest in rebooking the matchup.
"He's a very strong opponent, veteran," said Overeem, regarding Oleinik. "We've trained together. He's a friend and I didn't like to fight him. I was originally scheduled to fight Alexander Volkov. The fight did not happen tonight, but I'm very open to that fight in the future."
Despite the conclusive result, it was not an easy win for Overeem by any stretch. Oleinik, 41, has been calling for a big-name opponent for some time, and he came out of the gates fast.
He tagged Overeem with a looping, overhand right early on, and did well pressuring Overeem along the fence. He landed several long sequences of punches to Overeem's body after repeatedly walking him back. Although Overeem remained calm and clear-eyed throughout, it was clear the pressure had some effect on him.
Oleinik's 6-foot-1 stature, however, ultimately played perfectly into the 6-foot-4 Overeem's Thai clinch. He landed several hard knees to Oleinik's midsection before elevating those attacks to the head for the finish. It is the 24th knockout win of Overeem's storied career.
Makhachev out-grapples game Tsarukyan
Lightweight contender Islam Makhachev (17-1) earned his sixth win in a row, as he out-wrestled Arman Tsarukyan (13-2) in a high-level grappling affair. All three judges awarded Makhachev the decision victory: 30-27, 30-27 and 29-28.
Makhachev, a teammate of lightweight champion Khabib Nurmagomedov, defended the majority of Tsarukyan's attempts to drag him down and consistently won the key positional battles. He dropped for a tight guillotine in the opening round but did not appear close to a finish otherwise.
It was a significant win for Makhachev, though, and his first since July. Tsarukyan, of Armenia, dropped his UFC debut but is nevertheless a name to keep an eye on moving forward.
Pavlovich picks up quick KO
The finish came courtesy of a right cross. Pavlovich rocked Golm with a stiff jab in the center of the cage, and then followed it with a hard right hand. Wounded, Golm retreated to the fence and put his guard up, which allowed Pavlovich to pick his shot and wrap the right cross around Golm's defense.
It is the 11th win by knockout in Pavlovich's career. He is 1-1 in the UFC, having lost to Alistair Overeem in his promotional debut last November.
Modafferi upsets Shevchenko sister
Veteran flyweight Roxanne Modafferi (23-15) upset Antonina Shevchenko (7-1) via split decision in a hard-contested bout. Two judges saw it 29-28 for Modafferi, while a third had it 29-28 for Shevchenko. ESPN scored the bout 30-27 for Modafferi.
Modafferi, who fights out of Las Vegas, was a sizable underdog going in, but she surprised Shevchenko with a very efficient ground game. She converted five of six takedown attempts, according to UFC Stats, and out-landed Shevchenko in total strikes 105-87.
Shevchenko, who is the older sister of defending flyweight champion Valentina, had some moments late and out-landed Modafferi 64-33 in significant strikes, but she simply could not stay on her feet enough to build momentum. She falls to 1-1 in the UFC, while Modafferi improves to 2-3.
Makhachev takes unanimous decision vs. Tsarukyan
Islam Makhachev holds off Arman Tsarukyan to win by unanimous decision. For more UFC action, sign up for ESPN+ at https://plus.espn.com/ufc.
Jotko snaps three-fight skid
Jotko, 29, proved to be in another class than Amedovski on the floor. He took the UFC newcomer down in each of the three rounds, scoring with punches and elbows. He trapped Amedovski in a crucifix position in the second round, and he probably would have earned a finish had the clock not run out.
The win is Jotko's first in four appearances. He began his UFC career with a promising record of 6-1 before dropping three straight.
Jotko defeats Amedovski via unanimous decision
Krzysztof Jotko uses takedowns and punches to beat Alen Amedovski by unanimous decision. For more UFC action, sign up for ESPN+ at https://plus.espn.com/ufc.
Evloev, a former M-1 bantamweight champion fighting at featherweight in his UFC debut, remained undefeated in his professional MMA career with a smothering grappling display that produced a decision win that was as decisive as they come.
Evloev (11-0) had a point deducted in the second round for an illegal knee to the head of a grounded Choi. But the fight went on, and the 25-year-old Russian never let up, controlling South Korea's Choi (7-2) the whole way to earn 29-27, 29-27 and 29-26 scores from the judges.
Evloev wins by unanimous decision vs. Choi
Movsar Evloev gets the best of Seungwoo Choi and wins via unanimous decision. For more UFC action, sign up for ESPN+ at https://plus.espn.com/ufc.
Aliev, who generally relies on his brawny wrestling game, gained the respect of Nakamura early with some crisp boxing. Even as Nakamura weathered the early story, when the fight turned in to a grappling contest, Aliev maintained control there as well, earning a clear decision win along the way.
Aliev (15-3) used a fast jab to keep Nakamura (34-10-2, 1 NC) out of striking rhythm and led the dance the whole way in the his strongest UFC showing yet. All three judges scored the bout 30-27 in the Russian's favor.
In his first fight since 2016, Yakovlev fended off several early offensive pushes from Da Silva and then, as Round 2 was heating up, Yakovlev dodged a takedown attempt. When Da Silva persisted, the Russian dropped some elbows to Da Silva's head before sinking in a choke to get the tap-out at 3:10 of Round 2.
Yakovlev (24-8-1) started the final sequence by slamming Da Silva (20-2) to the mat, but the Brazilian, who was making his Octagon debut, scrambled in an attempt to reverse position. The 6-foot-3 Yakovlev had the length to maintain his position, however, and eventually he secured a variation of a guillotine and anaconda choke.
Aliev beats Nakamura by unanimous decision
Sultan Aliev and Keita Nakamura battle for all three rounds, but Aliev wins by unanimous decision. For more UFC action, sign up for ESPN+ at https://plus.espn.com/ufc.
Abdurakhimov caught Tybura with a left hook to the temple that wobbled him, then followed Tybura across the Octagon and launched a flurry of punches as his opponent sagged against the cage, until the referee jumped in at 3:15 of Round 2.
The heavyweights engaged in a stand-up battle all the way, with Russia's Abdurakhimov (20-4) landing more consistently until Tybura (17-5) starting timing his counter punches. The finish came when that sweeping hook caught Tybura flush on the right temple, and his equilibrium left him. This was Abdurakhimov's third straight victory.
Oleksiejczuk made a quick turnaround because his last fight, in February, lasted barely a minute and a half. This time he needed even less time to get the KO, catching the aggressive Antigulov early and dropping him three times in a fight that lasted just 44 seconds.
Oleksiejczuk (14-2), a 24-year-old out of Poland, is unbeaten in his past 12 fights, and Antigulov (20-6) lost his second in a row after a 14-fight winning streak.
Mustafaev, who had not fought since 2016 because of an arm injury, didn't have much of an opportunity to test that arm because he made quick work of Fiziev with a spinning back kick -- flooring the Kazakhstan fighter and finishing him just 1:26 into the fight.
It was the first MMA loss for Muay Thai specialist Fiziev (6-1), who was grazed by the first kick Mustafaev launched, then was knocked down and dazed by the second. Mustafaev (15-2), who is from Dagestan, finished the job with a flurry of punches on the canvas.
Jeff Wagenheim contributed to this report.