Holly Holm has shocked the world, knocking out Ronda Rousey in their UFC bantamweight title fight at Melbourne’s Etihad Stadium.

The 34-year-old Holm, a multiple boxing world champion, delivered a head kick 59 seconds into the second round of the bout to send Rousey crashing to the canvas.

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It appeared Rousey was close to unconscious as she hit the deck.

Rousey was taken to hospital after the fight and treated for facial cuts.

She skipped the post-fight press conference, with UFC boss Dana White saying she was down after the defeat.

“She was transported (to hospital) because she got knocked out,” White said.

“Obviously she’s completely bummed out and depressed.”

“These are the moments in fighting that make it so crazy and so fun.

Holm appeared to be in shock at what she had achieved.

“I don’t know … I am trying to take it in … but it’s crazy, isn’t it?” Holm said.

“How could I not do this? I had the best coaching from stand-up, to grappling, to wrestling. This team right here is priceless.”

Holm, who had achieved eight of her previous MMA victories by knockout, but had gone the distance in her two UFC fights, said head kicks to Rousey were the plan.

“I didn’t want to kick her in the body and have her trap my leg … I went high and got it,” Holm said.

The win propelled Holm’s MMA record to 10-0 and dropped Rousey’s to 12-1 as UFC commentator Joe Rogan called it the biggest upset in the sport.

Rousey appeared out of sorts from the beginning, refusing to touch gloves to start the fight – something she had only done once before, against arch-rival Miesha Tate.

Rousey then proceeded to go all-out in attack, chasing Holm all over the octagon in the first round, to her detriment.

While Holm waited for her chance, fighting off the back foot to land strikes as Rousey rushed her, Rousey wore more than a few, including a big elbow and a hard straight left in the opener.

Rousey couldn’t even sink her trademark armbar in when she went for it two minutes into the fight.

The judoka took Holm to the canvas but she fought out of the predicament, quickly rising to her feet.

– AAP

Watch the KO below:

The 3 punches Holm landed after Rousey was already clearly out cold = my problem with MMA pic.twitter.com/er3wlK9yzE

— Alex McClintock (@axmcc) November 15, 2015