In what’s been called "the biggest upset" in Ultimate Fighting Championship history, Rousey was knocked out by 34-year-old Holly Holm in the second round of their title bout in Melbourne on Sunday.

Holm, a former world champion boxer from New Mexico, delivered a powerful kick to Rousey’s head 59 seconds into the second round. The blow sent Rousey toppling to the canvas.

According to the Agence France-Presse, the 28-year-old California native, who had been undefeated through 12 UFC fights prior to Sunday's bout, appeared to be "close to unconsciousness as she hit the deck."

Rousey, a former judo Olympian, was reportedly whisked to the hospital following her knockout loss to receive treatment.

MMA Fighting’s Ariel Helwani said that Rousey had a "busted lip," but "no serious injuries."

"Obviously, she's completely bummed out and depressed," UFC President Dana White told MMA Fighting of the former champ.