The post-fight showdown was about as textbook as the one-sided win by the undisputed middleweight champion Claressa Shields over the challenger Ema Kozin in Cardiff, Wales, on Saturday.

As Shields, an unbeaten 26-year-old who outboxed and outclassed Kozin over 10 rounds, was analyzing the fight with an interviewer at ringside, Savannah Marshall and her promoter joined the conversation. Marshall, who is also undefeated as a professional, beat Shields in an amateur bout in 2012, and the two boxers could meet in a big-money rematch later in 2022. Last year, Shields, a two-time Olympic gold medalist from Flint, Mich., signed a two-fight deal with Sky Sports that brought her $1 million guaranteed, along with the promise of a bout against Marshall.

The unanimous decision win over Kozin improves Shields’s professional record to 12-0 with two knockouts.

When asked to assess Shields’s performance, Marshall, who lives and trains in Hartlepool, England, opted for an insult.

“If you perform like that against me, I’ll absolutely wipe the floor with you,” said Marshall, who is 11-0 with nine knockouts as a professional.

Shields leaned in toward the interviewer so he could clarify what Marshall had said, the challenge briefly lost between Marshall’s thick northern English accent and Shields’s American ears. But once it registered as trash talk, Shields knew how to respond.

“You can’t wipe my drawers,” Shields said.

From there, the two boxers started the kind of mutual jaw-jacking that sells fights months before the opening bell. Shields’s promoter, Dmitriy Salita, and Marshall’s backers at the promotional outfit Boxxer, which is based in the United Kingdom, believe that a Shields-Marshall bout would be the most significant women’s boxing match ever. But that bout, tentatively planned for later this year, depends on Marshall winning her next fight, on March 12, against Femke Hermans.

Shields earned her place in a future megafight on Saturday, winning every round on every judge’s card against Kozin, a Slovenian fighter nicknamed “The Princess.”

“I give myself an A-minus,” Shields said. “The only thing I didn’t do was get the damn knockout.”

On paper, Kozin figured to pose a challenge. Like Shields, she stands 5-foot-8 and weighed in just below the middleweight limit of 160 pounds. She is also a southpaw who has recorded 11 knockouts in 21 wins.

But in the ring, Shields outclassed her.

When Kozin spent the first round advancing, Shields patiently retreated and counterpunched. Midway through the first, Shields landed two hard right hands to the body. Just before the bell, she connected with a straight right and left hook to the head.

In the fourth, a pair of straight rights to the face made Kozin grimace. The next round, a flurry of punches from Shields prompted Kozin to wrap the champion in a clinch. At the bell, Kozin made a slow, slump-shouldered walk back to her corner.

Each successive round convinced Shields’s team that Kozin would not last the 10-round distance.

“Don’t rush it,” said John David Jackson, Shields’s trainer. “You can get her out.”

Marshall watched from ringside, looking bored. When she saw herself on the broadcast’s camera she pretended to fall asleep, suggesting she was unimpressed by Shields’s failure to knock Kozin out. By then, the fight’s broadcast crew was already speculating on a venue for a Shields-Marshall title fight, suggesting a soccer stadium or the O2 Arena in London.

Barring the plot twists that often derail significant fights that seem certain, Shields and Marshall should fight later this year. But is their hypothetical bout the biggest women’s fight ever?

Like all boxing titles, that claim is disputed.

Laila Ali and Christy Martin were the biggest names in women’s boxing when they fought in 2003. But the 35-year-old Martin had to jump three weight classes to meet the 25-year-old Ali, who won by knockout in four lopsided rounds.

On April 30, Amanda Serrano and Katie Taylor will meet in a bout their promoters are calling the biggest women’s fight in history, because each fighter is guaranteed at least $1 million, and because they will become the first women to headline a show at the main arena at Madison Square Garden in New York.

For their part, Shields and Marshall have personal history. In March 2012, Marshall defeated Shields 14-8 under the old computerized scoring system. That summer, Marshall lost her quarterfinal bout at the Olympic Games, while Shields won her first Olympic gold medal.

Shields has not lost a boxing match since that defeat to Marshall. According to the scorecards of her professional bouts, she has not lost a round since 2019, when she won a unanimous decision over Christina Hammer, with all judges scoring the bout 98-92. On Saturday, Shields battered Kozin for 10 rounds, leaving an impression even if she did not score a knockout.

“She’s gonna feel it when she goes home,” Shields said.