British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a match where the styles never quite clicked, with frequent clinching spoiling the contest.
Two judges scored it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but what defines champions? They win," the victor said in the ringside as he was faced boos from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts felt the challenger, thirty-one, merited the decision but the contender endured the second setback of his 28-fight professional journey.
Buatsi Claims Win in Slow Encounter
Buatsi's progress has slowed in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter ready to overcommit in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance decreased during frequent holding, with Parker falling to the floor various instances during grappling.
Parker closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry battle to win the European light-heavyweight belt.
The arena became quiet for a deeply poignant tribute prior to the bout as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the premier televised match card in the city since Hatton's death. As the concluding sound faded, the silence transitioned to a shout of "there's just one Ricky Hatton".
The action during the bout matched the emotion. The eventual winner was sent to the canvas by a significant blow flush on the face in the early round, rising shakily to his footing on the eight count.
But the traditional red equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up quickly, significant bruising forming under his face as the duo landed punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the verdict with official scores of even score, close margin and 115-112, but both fighters were determined and courageous, everything their hero the legend represented.
