Julianna Peña didn't even realize Amanda Nunes had tapped out of Peña's chokehold until somebody told her in the cage moments after the referee pulled her off the long-reigning champion.

One of the biggest upsets in UFC history might have been a surprise in the moment for Peña, but she had never stopped believing she could do the nearly impossible.

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"Everybody was sleeping on me, and I shook up the world and did exactly what I said I was going to do," Peña said. "But I’m not surprised. I have a big heart and determination."

Peña stopped Nunes by submission with a rear naked choke in the second round at UFC 269 on Saturday night, claiming the bantamweight title from the long-reigning two-division champion in a 10-to-1 upset.

Charles Oliveira also defended his lightweight title for the first time with a third-round stoppage victory over Dustin Poirier by standing rear naked choke in the main event.

But the night belonged to Peña (11-4), who was a massive underdog against a vaunted opponent widely considered the greatest fighter in the history of women's mixed martial arts. Nunes had won 12 consecutive fights since 2014 and reigned simultaneously atop the 135-pound bantamweight and 145-pound featherweight divisions for three years.

"Amanda has been such a great champion, and she’s done a ton for the sport," Peña said. "For me to be able to take out arguably the greatest of all time is something that’s still sinking in right now."

After Nunes largely dominated the first round with two knockdowns and superior striking, Peña shockingly hurt Nunes with punches in a slugfest start to the second round. Peña then got Nunes to the ground, got her back and forced the champion to tap out with a choke around her neck with 1:38 left.

"It feels crazy," Peña said. "I definitely expected to win, but the world is my oyster."

Peña had won just two of her four fights over the past 5 1/2 years, and the Spokane native who trains in Chicago got the title shot as one of the few legitimate 135-pound fighters that Nunes hadn’t already beaten. Peña didn't fight for 30 months from 2017 to 2019 while giving birth to her daughter, but she won two of her three ensuing bouts to get this shot.

"Julianna is a person who always believed in herself and believed that she could win this fight if she got it," UFC President Dana White said. "You heard her for months leading up to this fight, and she did it. It’s one of the things that makes this sport so incredible. An upset like this, where you can't believe it, it happens all the time here."

Nunes was fighting for only the third time in two years after making two featherweight defenses since her most recent defense of her bantamweight belt in December 2019. Few opponents had even given her a stiff challenge since her second victory over current flyweight champ Valentina Shevchenko by split decision in 2017.

Nunes is almost certain to be granted a rematch with Peña, who is eager to grant it: "We can do it next week. I'm free next week. I'm free next month."

After Peña's upset, Oliveira (32-8, 1 no-contest) survived a rough fight with Poirier (28-7, 1 no-contest) to improve to 10-0 with nine stoppage victories since 2017.

Poirier battered the champ with punches in the first round and knocked him down twice, but Oliveira took control on the ground in the second round with a series of vicious elbows. He finished the fight with 3:58 left in the third by attaching himself to Poirier's back and forcing him to tap while standing up.

"We respect each other a lot," Oliveira said through a translator. "But I was going to have my arm raised, and that's what happened. ... I want to make history. I want to leave a legacy, and I plan to show people that I can."

Oliveira finally claimed the belt last May in his 28th UFC fight -- the longest wait for a title in the promotion’s history and the culmination of an epic journey by a Brazilian veteran who overcame poverty and childhood illness to become an elite jiu-jitsu practitioner and mixed martial artist.

Oliveira set the UFC record for stoppage victories by beating Michael Chandler with punches, and his finish of Poirier increased the record to 18. Oliveira’s 10-fight winning streak is the second-longest active string in the UFC, trailing only Kamaru Usman’s 15 straight.

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Oliveira and White both said the champ's next defense is likely to be against Justin Gaethje, the entertaining brawler who held the interim title in 2020.

Poirier already had a spectacular 2021 with his two victories over Conor McGregor, erasing the vaunted former champion’s winning mystique and making two enormous paychecks for decisive stoppage wins. Poirier's only other loss in his last 11 fights since 2016 was to Khabib Nurmagomedov, who took away Poirier's interim lightweight title before retiring undefeated.

"It ruins the dream outcome that I had planned, to forever be a world champion after tonight," Poirier said. "But the year isn’t ruined. An opportunity I had is ruined, and that’s all right. It is what it is. I’ll look in the mirror like a man."