When Julianna Pena submitted Amanda Nunes in December, it was considered arguably the biggest title upset in UFC history.

Given Nunes’ (21-5 MMA, 14-2 UFC) status as who many considered the greatest women’s fighter in history, and the fact she held two belts when she lost the 135-pound title to Pena, a rematch is a strong likelihood with new champ Pena (11-4 MMA, 7-2 UFC).

In fact, UFC president Dana White said he thinks a rematch “will probably be the biggest women’s fight of all time.”

Felicia Spencer, who recently announced her MMA retirement, knows a few things about Nunes. She went five rounds with her in a title fight at UFC 250, and though she didn’t win any rounds against her, she learned enough to know upsets always are possible.

“I always know there’s a chance for the underdogs to win,” Spencer told MMA Junkie. “I’ve been in that position so many times, and I was 100 percent confident that I could pull it off. It just takes a few mistakes in a fight, or one mistake, for that to happen.

“Did I expect it to happen, personally? I wasn’t betting on it, no. But I feel like Julianna had the moment where she could capitalize on a mistake of Amanda’s. Amanda reacts certain ways when she gets hit, and it’s a trend there. We’ve seen her get rocked in certain ways and then make more bad decisions. So Julianna did a good job making that happen in the fight.”

If – or perhaps when – that rematch gets booked, Spencer said she’d put her money on Nunes. And she said she’d do so an overwhelming amount of the time.

“I would lean Amanda because I feel like for so many fights, she was able to avoid making a mistake like that,” Spencer said. “I feel like she’d be able to be in a mindset to do it again – to have a sort of flawless performance, if you want to call it that. But again, anything can happen in that cage.

“I wouldn’t be surprised if she lost (again), but if I had to lean one way, I’d lean on Amanda eight out of 10 times.”