A pair of unification bouts will grace one of the best shows of an already incredible year in boxing.

BoxingScene.com has confirmed that the previously announced Mikaela Mayer-Alycia Baumgardner junior lightweight championship clash will head overseas, due to take place September 10 at The O2 in London. The bout will be paired with the Claressa Shields-Savannah Marshall undisputed middleweight championship, with the show to air on an ESPN platform in the U.S. and Sky Sports in the UK.

Mayer’s IBF/WBO titles and Baumgardner’s WBC/IBO belts will be on the line in a bout to officially crown a true junior lightweight queen.

ESPN.com’s Michael Rothstein first reported that the event was finalized, confirming a previous breaking news report from the Ring IQ Boxing Talk YouTube channel revealing that Mayer-Baumgarder was London-bound. BoxingScene.com has learned that both bouts are expected to be formally announced on Tuesday following Independence Day holiday weekend.

The show will see 2016 U.S. Olympic teammates Mayer and Shields share the stage for the first time in the pros. The longtime friends and current unbeaten champions were the lone two females on the 2016 team that traveled to Rio, where Shields captured her second consecutive Gold medal.

Mayer stuck around in the amateur ranks for another year before signing with Top Rank upon turning pro in 2017. She has since emerged as a pound-for-pound level talent, winning the WBO title in a ten-round masterclass against unbeaten champ Ewa Brodnicka in October 2020. Two fights later, Mayer outslugged Maiva Hamadouche in their epic IBF/WBO unification bout last November in Las Vegas which was hailed by BoxingScene.com as the 2021 Female Fight of the Year.

In her most recent start, Mayer pitched a ten-round virtual shutout of former featherweight titlist Jennifer Han this past April 9 in Costa Mesa, California. The bout marked her first headliner in her childhood home state, having grown up in Los Angeles before relocating and eventually settling in Colorado Springs.

Each of Mayer’s last two fights came one week prior to Baumgardner entering the ring, their aligned schedules making it that much easier to move forward with their mouthwatering fight.

In a weird way, the bout almost represents a home game for Baumgardner (12-1, 7KOs), who will now fight in the U.K. for the third straight time. The explosive puncher-boxer from the greater Detroit area crashed the title picture with a sensational fourth-round knockout of unbeaten WBC/IBO champ Terri Harper last November 13 on the road in Sheffield, England. The feat was recognized by BoxingScene.com as the 2021 Female Knockout of the Year.

Baumgardner followed up with a ten-round shutout of former featherweight titlist Edith Soledad Matthysse this past April 16 in Manchester, England.

There was a brief period where Baumgardner was poised to face WBA titlist Hyun Mi Choi, as both titlists are promoted by Matchroom Boxing. The theory at the time was to stage that fight first “and then Mayer for all the marbles” as previously told to BoxingScene.com by Matchroom Sport chairman Eddie Hearn.

Those plans took a drastic turn when Mayer and Baumgardner were able to turn their fierce rivalry into one of the year’s most anticipated fights. Terms were reached in May, with the event merely announced as taking place in September on an ESPN platform. Las Vegas was the one U.S. city targeted, though there always existed the strong possibility of the bout landing in London as part of Top Rank’s continued working relationship with Ben Shalom’s BOXXER promotional company in the U.K.

The terrific grudge match lends a tremendous boost to a show already topped by the long-awaited showdown between Shields (12-0, 2KOs) of Flint, Michigan and Hartlepool, England’s Marshall (12-0, 10KOs).

Shields has won championships at 168, 160 and 154 pounds—in that order and undisputed championship status at middleweight and junior middleweight. The move down to 154 came at the cost of Shields letting go of her WBO middleweight title, which was claimed by Marshall in a seventh-round knockout of Hannah Rankin in October 2020.

Marshall has scored eight straight knockouts, including a three-round blitzing of Femke Hermans on April 2 in Newcastle, England. The 31-year-old Brit is the only fighter to beat Shields pro or amateur, doing so more than ten years ago during the Round of 32 in the 2012 World Amateur Championships. Marshall won the tournament outright, earning a place on the 2012 Great Britain Olympic boxing team that competed in London.

Jake Donovan is a senior writer for BoxingScene.com. Twitter: @JakeNDaBox