A split decision went to Jonas. One judge scored it widely to Mayer, 97-93. But the other two had it to Jonas on a narrower margin, 96-94 and 96-95.

Mayer, fighting for a world title for the first time since her bitter unification defeat to Alycia Baumgardner, was desperate to win a major championship once again.

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Hometown favourite Jonas, defending the IBF welterweight crown, was already a two-weight champion.

But she was looking to burnish her legacy and secure the most meaningful victory of her career so far.

Both knew too that victory and that championship win was a ticket to more major fights too.

Jane Couch, the trail blazer for women's boxing in the UK and now a Hall of Fame inductee, fittingly processed Jonas' title belt to the ring.

Welcomed to the ring by a tremendous ovation, Jonas made a positive start, ripping a spiteful combination body shots into Mayer's midriff.

Although Mayer was stepping up to welterweight for the first time, she was taller and worked from range, a left hook setting up her cross.

In the second round a hard left hook struck Jonas, but it was wide-swinging right that forced the Briton to back up a step and blink.

These were strong attacks from the American and Jonas had to backpedal again when Mayer drove a hard right into her stomach.

Using her footwork, Jonas moved from side to side, trying to get herself clear of the sudden danger.

She hammered mid range hooks back into Mayer, just to fend off the American before the end of the round.

Mayer was boxing a southpaw for the first time in a her professional career, but she was adapting to it and threatening all the while.

A Mayer right hook connected solidly in the next round too. But Jonas responded to that, timing her lead hook, hitting it to the head and screwing the right up into the body.

Jonas uncorked an explosive left hook, but Mayer still came on, setting up a firm lead left that curved round the champion's defences.

The Briton opened up with a tremendous attack to start the fifth round, the crowd's noise swelling behind those strikes.

Mayer though was undaunted and got herself back on the front foot. Jonas though caught her again with a short cross.

Mayer drilled in three punches to the head just at the close of the fifth round.

The American continued to work busily and the two traded punches out in the centre of the ring. She snagged Jonas on the end of a firm cross. Jonas though snapped in a jab as Mayer came forward.

She sank her back hand left into Mayer's body, but the American managed to maintain the pressure.

Mayer landed a long one-two and, heartened, pressed on. A cracking Jonas right hook though slammed into her challenger.

Jonas hacked a left hook down off the ropes, but Mayer still managed to jolt her. She lined up right crosses, those hard punches bursting through the champion's guard.

She appeared to hurt Mayer, momentarily, in the ninth round. The crowd sensed it as well and yet another roar resounded through the arena.

The champion however had taken punishment too. Her left eye had swollen up and Mayer's punches could fly through.

Brave to the finish, they let their hands go, crashing punches landing still right up to the final bell.