Julianna Peña's upset of Amanda Nunes stunned the MMA world

If you ever wondered how Buster Douglas' upset of Mike Tyson would have gone down in the age of Twitter, Saturday's shocker might be a decent approximation.

Amanda Nunes, the two-belt UFC champ and overwhelming pick as the greatest female fighter in MMA history, fell to heavy underdog Julianna Peña by second-round submission at UFC 269. Nunes had entered the fight as a -1000 favorite and Peña a +650 underdog via BetMGM.

The fight began with more of the same from Nunes' career: absolute dominance. Defending her bantamweight belt, Nunes landed plenty of shots in the first round before taking Peña to the ground and controlling the fight from there.

Things changed as soon as the second round began. Peña suddenly started landing jab after jab to Nunes' chin and the champion never seemed to find her footing from there. Peña eventually took her down and locked in a rear naked choke, triggering Nunes' first tap-out since the first fight of her career in 2008.

Even as it was happening, it didn't seem real, most of all to Peña, who seemed to have trouble processing what she had just done.

Meanwhile, here's how the broadcast booth was handling it:

The MMA fighters watching from home didn't do much better handling what may go down as the biggest upset in MMA history.

Not all of them didn't see it coming, though.

If anything, the person who handled it best was Nunes, who delivered an uncommonly gracious interview after Peña took her belt. It probably helps that she knows she'll get an immediate rematch.