Nunes, 33, lost her bantamweight title in one of the biggest upsets in UFC history.
Going into the fight, the Brazilian was as big as a 1/11 favourite with some bookmakers, but she quickly tapped out as soon as Peña sank in a rear-naked choke in the second round much to the surprise of those watching from the stands.
He said: “I can’t believe I got Peña right either.
“I got to tell you, man, that was a different fight. Like, we’ve seen upsets before.
“Even if you take Mike Tyson versus Buster Douglas where Mike is trying to get up, and he just can’t beat the count or when Ronda Rousey got her head kicked into the third row, but she didn’t want it to happen.
“This was totally different. Amanda flicked it. That was 100 percent mental beating, zero percent physical. That submission wasn’t there.”
Sonnen even went so far as to say Nunes ‘quit’ after Peña took her back and locked in the submission attempt.
The former UFC title challenger continued: “That was not a move. That was absolutely not a fighting technique. Julianna was in a terrible position, and Amanda quit.
“That’s okay. Everybody goes through that at some point. I only point that out not to kick her, I point that out because that’s what the surprise was.
“If she got kicked like Ronda did or knocked out like Mike did, we just chalk it up to a big upset and a glorious night.
“To mentally check out and hand it all back in only seven minutes, a bit of a surprise.”
Perhaps unsurprisingly, Peña respectfully disagrees, as she feels Nunes ‘had no choice but to tap’.
And the pride of Chicago was quick to point out this isn’t the first time she has employed that strategy to great effect.
She told MMA Fighting: “She had no choice but to tap.
“People want to say she quit – she didn’t quit, she was getting choked.
“She had no choice but to tap – I would have broken her neck.
“She tapped because she had no choice.
“[My coach] Rick [Little] and I have been working this choke for a while, and it was the same pretty much as I got with Sara McMann.”