All three judges ruled in the American’s favor, with scorecards of 96-94, 97-93, 97-93, as Shields’ relentless pace overcame Marshall’s longer reach and more powerful punches.
By beating Marshall, Shields avenged the only ever defeat that she has suffered during her professional and amateur career and confirmed the title she wears on her necklace - the GWOAT, Greatest Woman of All Time.
It was a historic night for women’s boxing, marking the first-ever all female card in the UK, as well as the first time two female boxers headlined at a major British venue.
“I want to thank Savannah Marshall and her whole team and the UK fans for being here because this is a special moment for women’s boxing,” Shields told Sky Sports.
“Here we are in front of 20,000 fans at The O2 Arena. It’s an unbelievable moment. It was a special night for women’s boxing and I think it was fight of the year.
“I know I did the most work today and was winning with those combinations. I did what I do in training and I got the job done.
“I have been working hard for a very long time and no one has given me credit.”
Both Marshall and Shields entered the fight with a 12-0 record, the former as the WBO titlist and the latter as the unified WBC, WBA and IBF 160lbs champion.
And the quality of both fighters was evident from the beginning, with flurries of punches replied with in kind during every one of the ten two-minute rounds.
Shields even revealed afterwards that she could not see out of her right eye after the sixth round, so hard were the blows struck by Marshall.
“Claressa is a brilliant fighter - not as fast as I thought! She has definitely earned the title of the Greatest Woman of All Time,” Marshall said afterwards according to Sky Sports.
“I want to say a massive thanks to everyone who bought a ticket, I really appreciate it.
“It’s amazing that two women have sold out the O2. It’s unbelievable and I thank everyone from the bottom of my heart.”
Before Shields and Marshall entered the ring, Alycia Baumgardner became the unified super-featherweight champions with a narrow victory over Mikaela Mayer.