When Miesha Tate broke into mixed martial arts 15 years ago, and for many years thereafter, the idea of appropriate weight classes for women wasn’t really a thing. Plenty of women like her took fights at 135 or 145 pounds, regardless of size.

“We just didn’t have the same opportunity or the amount of opportunities [at that time], so it was kind of take whatever opportunity you can get,” Tate recently told The Post over the phone. “And now, there’s options, so that’s really the biggest difference.”

At last, Tate (19-8, 11 finishes) has exercised her option to compete at 125 pounds for the first time when she faces Lauren Murphy in the main card opener of Saturday’s UFC on ABC event (2 p.m. ET) from UBS Arena in Elmont, N.Y. 

And the opportunity on the table, Tate believes, is the chance to earn a crack at flyweight champion Valentina Shevchenko with a victory over Murphy (15-5, nine finishes), who fights for the first time since a TKO loss to the champ in September. The former bantamweight champion “100 percent” believes a win on Long Island would net her a title shot.

Dropping down to 10 pounds from her typical weight class meant lifestyle changes. Tate said she was more “diligent” with monitoring her diet and counting calories. Workouts run longer at more than two hours. She credits Sam Calavitta, a founder of The Treigning Lab in California, with taking a hands-on approach with shaping her diet to safely compete at flyweight.

“I’ve had to make sure that I stay within a range that isn’t going to shut my body down and deprive me to the point where it’s causing problems or issues,” Tate described of her training camp. “So it’s been a very long camp because it had to be slowly done [with] very small, incremental changes that don’t cause stress on the body, but just allow me to naturally, slowly lose weight.”

Tate said she doesn’t feel the shedding extra weight she carried while competing at bantamweight will be to her detriment. At 125 pounds — at least for Friday weigh-ins, after which she expects to weigh “just north of 135” for the afternoon clash, which is hardly massive for the weight class — she feels quick.

Her cardio is much improved in her estimation as well, which Tate chalks up to carrying extra mass.

“That size doesn’t matter,” Tate says. “I’m still performing the same, if not better, pound-for-pound against the same people [in training]. It’s not like the strength has diminished and all of the sudden I feel small. No, I just feel really fast. I feel really quick. 

“And I feel like most of the things that I was trying to do were technique-based anyways. It’s not like I was trying to muscle everything.”

Although it took this long to make the move down in weight, Tate believes she “absolutely” would have considered doing so much earlier in her career if the flyweight division had been supported by major promotions. Women’s 125 pounds is the most recent addition to the UFC, with the inaugural title fight coming in December 2017 — 13 months after Tate retired from the sport.

After returning to competition last July with a TKO victory over Marion Reneau, Tate lost five-round decision to Ketlen Vieira in November. From her rivalry with former champion Ronda Rousey through the Reneau fight, she says she didn’ feel a “big strength discrepancy” between her and her opponents. That changed with Vieira.

“Ketlen felt really long and tall, and she felt heavy,” Tate recalls. “Just trying to move her around wasn’t easy.”

Following the defeat, Tate took UFC vice president of talent relations Mick Maynard up on his suggestion to move down to 125, an idea she said hadn’t been of interest to her — or, again, available — for the bulk of her career. She dismissed Maynard at first, reasoning that she didn’t need to be the bigger or stronger athlete in the cage to get the win.

“I’m just gonna be the better person,” she thought to herself. “But it’s a work harder, not smarter mentality. And finally, it dawned on me like, ‘You know what? If I was competing against the women that are 125 in my gym right now, those women feel so small to me. They’re so much easier to move around. Let’s give it a whirl because I just don’t want to have any what-ifs.’ ”