Holly Holm lands a blow against Ronda Rousey. (Joe Castro/EPA)

Just how did Ronda Rousey become arguably the biggest upset victim in UFC history after dominating her three previous opponents in a total of 64 seconds?

Despite being as much as a 20-1 favorite, Rousey (12-2 MMA, 6-1 UFC) never seemed into the UFC 193 bantamweight fight against Holly Holm (10-0 MMA, 3-0 UFC) on Saturday in Melbourne, Australia, and lost 59 seconds into the second round. It made for a wild scene and even Holm was having trouble grasping the magnitude of her accomplishment.

[A stunning second-round knockout]

“I’m trying to take it in, but it’s crazy,” Holm said (via MMA Junkie). “Getting in here, I had so much love and support. I felt like, how can I not do this with all that love. I had the best coaching, from standup to grappling to wrestling.

“Everything that we worked on presented itself in the fight. I haven’t spent this much time in the gym in my life. Everything we worked on happened tonight.”

[Holly Holm has a mantra]

Rousey ran into a buzzsaw of a boxer who left the sport for MMA, one who kept Rousey on her heels and rocking her with blows. A left kick to Rousey’s chin sent her to the floor of the Octagon and the fight was over. Rousey did not speak after the fight; she was taken to a local hospital, where she was kept overnight and was to have plastic surgery for a deep cut on her lip. Her camp said she had not suffered a concussion in the loss.

It was a stunning upset, with Rousey coming in talking about when she won, not if. No one gave Holm much of a chance, but her height and reach, as well as her boxing experience, were clear advantages. She was 33-2-3 as a boxer and 2-1 as a pro kickboxer, with an overall fighting record of 44-3-3. But this was only her third UFC fight.

“I wanted to be the first person male or female to cross over and be a champion in both sports,” Holm told ESPN’s  Ramona Shelburne, “and it hasn’t sunk in it but … it’s just surreal.”

Holm’s training for the fight was a contrast to Rousey’s. Holm worked out in New Mexico, where her husband runs a roofing business and expectations for her were far smaller than those for Rousey.

“It puts more pressure on her,” Holm told The Post’s Rick Maese. “I feel to me, it doesn’t really matter. … Trust me, I fear her — she’s the toughest, most dominating competitor out there. But she’s still just another female, just another person. There’s huge upsets in history for a reason. Somebody had to believe in themselves to get there.”

Now, inevitably, comes talk of the rematch. Rousey will have to balance her budding film career with UFC. She’s scheduled to film a remake of Patrick Swayze’s cult classic, “Road House.” Meanwhile Holm will be freer to focus. “Anybody who does come out with the victory should give the rematch,” Holm told Shelburne. “That’s how the sport goes and people are really going to want to see it. It’ll be a totally different fight the second time around, you know. I’m ready for it.”

Last month, on “The Tonight Show with Jimmy Fallon,” Rousey had an inkling how the fight might go.

“She’s the type of fighter you have to be very patient with,” Rousey said. “She’s going to try to keep distance and keep far away from me and keep me frustrated and to the point where I’ll make a mistake and she’ll try to kick me in the head–but it’s not going to go like that.”

Except it did.