A rivalry that had been brewing for 10 years reached a boiling point at the opening bell with both women charging into the center of the ring and unloading. But it was Shields who looked the better with a number of eye-catching combinations. 

After a fast start from Shields, Marshall went on the front foot in the second and looked to push Shields back onto the ropes. The American unified champion however used her impressive technical skills to escape any situation that could have posed any significant danger. 

As the fight progressed, Marshall slowly increased her work rate while Shields remained calm and stood firm as she managed to navigate the single shots the Hartlepool fighter was throwing. 

If Marshall was going to get the backing of the judges, she needed to throw more combinations, but this was proving difficult with Shields' slick movement. 

The tide seemed to have turned in the sixth with Shields showing possible signs of tiredness. She was frequently leaning on Marshall in an attempt to weather any attacks she may bring and even though Marshall was beginning to find more success, Shields showed no signs of being affected by her explosive power. 

After a brief resurgence from Marshall, Shields wrestled back control knowing she was ahead on the cards, and used a clever technique to frustrate her British rival who was told by her coach Peter Fury before the final two rounds to "Give it everything you've got".

As the final bell rang, both women received a huge ovation from a sell-out O2 Arena crowd who had witnessed a barnstormer of a fight between two of the world's best in women's boxing, but it would be Claressa Shields who would be crowned the undisputed champion at middleweight with all three judges scoring the fight in her favor, 96-94, 96-94 and 97-93. 

For Marshall, she let too many of the early rounds run away from her as Shields went toe-to-toe and utilized her exceptional footwork. Then when it came to increasing the pressure on the American, it was too little too late for Marshall. 

With Shields returning to PFL MMA after Saturday night's fight, it may be a while before we see her back in a boxing ring, but her fight with Marshall is one which she can look back on fondly, headlining a historic all-female card with a contest which captured the imagination of boxing fans old and new. 

Re-live the best moments from the O2 Arena in London below.