Julianna Pena has stopped Brazilian legend Amanda Nunes by submission in the second round at UFC 269 in Las Vegas, claiming the bantamweight title from the long-reigning two-division champion in one of the biggest upsets in recent UFC history.

American Pena (11-4) was a 10-1 underdog against the vaunted Nunes, 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.

After Nunes largely dominated the first round with two knockdowns and superior striking, Pena shockingly hurt Nunes with punches in a slugfest start to the second round.

Pena 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," Pena said. "I definitely expected to win, but the world is my oyster."

Pena had won just two of her four fights over the past five and a half years, and the Spokane native got the title shot as one of the few legitimate 135-pound fighters that Nunes hadn't already beaten.

Nunes was fighting for only the third time in two years after making two featherweight defences since her most recent defence 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.