Mikaela Mayer is now a three-division world champion.

She bossed proceedings from start-to-finish against defending WBA junior middleweight beltholder Mary Spencer, en route to a commanding points win on away soil in their Montreal Casino main event. 17-year professional judge Patrick Morley had her winning every round (100-90), while Gustavo Padilla and Benoit Roussel scored it 98-92 apiece after emptying the tank in a gruelling 10-round battle, but one she was in control of early.

Mayer, who holds the WBO welterweight strap, reaffirmed her desire to move back down for a proposed undisputed clash with unified beltholder Lauren Price in 2026 - but is open to floating between weight classes going forward, if the sanctioning bodies allow her.

"The most important thing is I have options and that's great in boxing, you always want options," she said in her post-fight interview.

"I came off two years of my career, took a left turn and had to get my way back to this position. I'd love to do both, defend my belts, become undisputed at 147 and come back up, defend at 154. It was a great experience and I can do both, we'll have to see what's best."

Natural welterweight Mayer (22-2, 5 KOs) looked determined in her divisional debut, as Spencer (10-3, 6 KOs) was unable to click into gear despite her best efforts on home soil.

There was no feeling out process between them as Mayer began the sharper of the two, digging punches to head and body early in a conscious effort not allowing Spencer to get into her rhythm and the 40-year-old was on frequently on her heels looking for counters.

Former boxer-turned-trainer Kara Ro implored Spencer to be busier and not worry about Mayer's fast start, match her in the jab department and use her physical strengths as the bigger woman. That proved easier said than done, Mayer unbothered by the power flying towards her and was persistent work downstairs and leading the bulk of their exchanges.

Spencer had some flashes of brilliant boxing in the final half-minute of round four, spinning Mayer off the ropes and landing two right hands, but that moment wasn't enough to give her much confidence as Ro warned her about the optics - being made to look second best.

Right on cue then, Spencer used timing and her penchant for uppercuts to pitch her best frame in the fifth. Both had success in the pocket, Mayer warned by referee Michael Griffin after landing a two-punch combination low after he told them to break.

Mayer's volume intensified in the sixth, Spencer much less so as infrequent left hooks by the champion were effectively being nullified by an avalanche of pressure firing back at her.

"Took that round off, you've got to step it up now," the Spencer corner stressed but their fighter was being outworked and couldn't stem the flow, Mayer had found her momentum and this smaller ring wasn't allowing the champion to create separation behind her jab.

The challenger chained together four hellacious left hooks in the final seconds of round eight, and things only became more dominant in an assertive ninth as Spencer couldn't get out of the way nor deter Mayer's heavy-hitting sequences from landing flush on her face.

Bloodied and cut over her eye, there was to be no miracle in the final frame for an increasingly weary champion as Mayer threatened a stoppage on an evening where she enhanced her legacy once more during a fight she didn't need to take.

In the evening's co-feature, super middleweight prospect Wilkens Mathieu did exactly as he promised to look sharp and spiteful en route to an invaluable 10-round decision win against Shakeel Phinn, warming up the Montreal crowd before the main event.

98-91 twice and 99-90 were rather wide scorecards which didn't tell the full story though.

He needed to navigate through some hairy moments too, from round eight on, after absorbing a howitzer of a right hand - which set the wheels in motion for Phinn's spirited second wind to take over and question the youngster's conditioning.

Having floored the longtime contender and threatened a finish in round three, Mathieu teed off with combinations and frantically pressed on the accelerator in the seventh.

However, he was also guilty of punching himself out, thinking he'd done enough to have the contest waved off by referee Martin Forest and that allowed Phinn a golden opportunity to throw him into deep waters.

He did exactly that early in the eighth, landing big right hands that pinged the 20-year-old back against the ropes and a nervous hush shrouded Montreal Casino as the 'Jamaican Juggernaut' went to work, pressing forward intently.

Mathieu refused to waver and risked his defensive shape firing back, much to the crowd's delight, though Phinn acquitted himself well down the stretch in an important learning experience for the Ring ambassador to have banked at this stage of his career.

Elsewhere, highly-ranked junior welterweight contender Arthur Biyarslanov (20-0, 16 KOs) stayed perfect with a solid points win over former world champion Sergey Lipinets, one where he needed to hold his nerve late after banking most of the earler rounds.

Eight months after being dropped and stopped in nine rounds by rising talent Adam Azim, the stubborn Kazakh returned here and gave as good as he got during a respectful, competitive clash largely fought in close quarters.

Whenever there was sustained distance between them, Biyarslanov made him pay and logged a third-round knockdown for his troubles as the 36-year-old was bloodied and his left eye quickly closing as they entered the final stages.

It was there though, that he produced a startling final round and threatened to recover an unassailable deficit with a knockout after wobbling Biyarslanov with clean combination punching up against the ropes. That proved a false dawn, though the Russian-born southpaw had to bite down on his gumshield and weather a bloodied storm to prevail.

Super middleweight: Wilkens Mathieu UD10 (98-91, 98-91, 99-90) Shakeel Phinn

Junior welterweight: Arthur Biyarslanov UD10 (97-92, 99-90, 96-93) Sergey Lipinets

Welterweight: Christopher Guerrero UD10 (99-1, 97-93, 98-92) Williams Andres Herrera

Light heavyweight: Mehmet Unal TKO1 Ralfs Vilcans

Junior light: Logan Clouthier UD8 (78-72, 78-72, 79-71) Thomas Chabot

Junior lightweight: Erik Israelyan SD4 (40-36, 36-39, 39-37) Dylan Schroeder