Claressa Shields and Savannah Marshall first became acquainted in Qinhuangdao, China in 2012.

Marshall outpointed a 17-year-old Shields on her way to winning gold at the AIBA Women’s World Boxing championships.

They renewed hostilities a decade later. Almost 20,000 fans turned up at London’s O2 Arena to see the brilliant Shields get her revenge, outboxing and outfighting Marshall to become the undisputed middleweight champion of the world.

The pair’s long-running rivalry takes an unexpected turn this weekend. 

On Saturday night, undefeated three-weight world champion and professional mixed martial arts fighter Shields will be in Newcastle, England, where she will watch Marshall make her own MMA debut against Mirela Vargas.

Shields is currently building herself up for her July 27 fight with WBC heavyweight champion Vanessa Lepage-Joanisse, and is constantly looking for new challenges. She understands that she will gain absolutely nothing if Marshall’s decision to follow her into the Professional Fighters League proves to be a bad one.

“Honestly, I want to see her go out there and be great,” Shields told BoxingScene. “We’re both representing women’s boxing, so if she goes out there and loses – especially if she loses in spectacular fashion – it kind of makes all of us in women’s boxing look bad, because she’s one of our top girls, to be honest. She’s our knockout artist.”

“She’s got one defeat – to me – but she’s coming into MMA and people expect her to get the knockout and still win, even though it’s an entirely different sport.”

Shields, 29, knows all too well just how different the two sports are. She hasn’t come close to losing a boxing match since that amateur defeat to Marshall, but she picked up an MMA loss in just her second fight in the cage.

Although undisputed super middleweight champion Marshall will be competing under a totally different ruleset and in an alien environment on Saturday night, Shields – who is now 2-1 in the cage – believes that Marshall will be most taken aback by just how much of an MMA fight is fought inside one’s own head.

Whereas she and Marshall have been boxing for so long that there will be times when they actually have to fight against their natural instincts and muscle memories, Shields says that Marshall will need to think her way through every second of her MMA debut. 

“It’s a mental game,” Shields said. “She’ll be surprised when she gets in the cage and hears that ‘click-click’ and they lock you in the cage.

“I think she’ll be surprised that her opponent won’t respect her punching. They never do. Their whole game is to take 20 shots just to get that one takedown on you and then you’re on the ground for the rest of that round.

“You have to switch between so many fights and you have to realize what type of fight you’re doing. You can’t be trying to box when you’re on the ground while the other person is doing jiu-jitsu. You have to change with them and compete on every level.”

A couple of weeks ago, Marshall told BoxingScene that she had fallen in love with the grappling part of her training and will continue to roll and pursue her belts in Brazilian jiu-jitsu long after she has finished boxing.

Although grappling forms an integral part of any MMA fighters arsenal, Shields believes that Marshall should do everything in her power to ensure it remains a hobby and something she uses only when absolutely necessary. 

The fact that both of Vargas’ defeats have come by submission suggests that Marshall should spend longer on her feet than on the ground this weekend, but – as Shields found out in her only defeat – grappling doesn’t take place only on the mat.

Her opponent, Abigail Montes, used her wrestling and clinch work to press Shields against the cage, and the constant threat of being taken to the ground meant that the GWOAT spent more time worrying about overhooks, underhooks and keeping her hips heavy than jabs, right hands and left hooks.

Shields learned that, for a boxer, landing hard shots quickly is a crucial part of maintaining a safe distance and making sure that your opponent is the one who ends up second-guessing themselves.

“Savannah’s a big puncher,” Shields said. “I was taught from very early on that when you’re fighting against somebody who’s really good on the ground, the more you punch them, the more those belts rankings go down.”

“Black belt. Hit ‘em twice, now it’s a brown belt. Hit them again and it’s a purple belt. Blue belt. You keep hitting them and they’ll forget all their techniques because they’re in such survival mode. That’s why I go out there in the first round and let my hands go, so that these girls know, ‘I will punch you in your damn face.’ 

“You’ve gotta have the confidence to do that and not worry about being taken down, because the way that we stand in boxing makes us suckers for being taken down.

“I know we see interviews where she says she loves grappling and stuff like that, but we really have to see her inside the cage and we’ll see what she loves. It’ll show if you love grappling when you’re getting taken down and you’re on your back while the girl’s going for submissions and trying to choke you. Then we’ll see if you love grappling.”

Marshall has said that the possibility of another fight with Shields was a major factor in her decision to sign with the PFL, but although Shields will be an interested observer this weekend, she isn’t necessarily using the trip as a scouting mission.

It would be a shame if the only stage on which two of female boxing’s biggest stars could find to settle their differences was inside an MMA cage, but – for Shields anyway – that isn’t a consideration. For the time being at least, it sounds like if it does happen, a third fight between the pair would take place in a boxing ring.

“We were supposed to rematch in boxing in the USA,” Shields said. “I think Savannah’s scared to come to my hometown, even though I came to hers and we fought there.

“I don’t have Savannah on my radar when it comes to the PFL because she’s not the PFL world champion. That’s my overall goal.

“I think to feel like ‘I want a fight with Savannah and to beat her’ is too small of a goal to have. I’m going for the bigger things, and that’s the million dollars and the belt – to say I’m PFL world champion on top of a boxing world champion. That’s a dream of mine that I feel like would be like winning the Olympic Games again.”