UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round contest at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the styles never quite clicked, with excessive holding marring the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Some ringside observers felt the challenger, thirty-one, should have been awarded the decision but the contender endured the second defeat of his 28-fight professional journey.
Buatsi Claims Victory in Uneventful Encounter
Buatsi's progress has plateaued in recent years through contract problems and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the better rounds.
The audience's tolerance decreased amid frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the supporting bout, Arthur overcame Rea by divided decision in a excellent local rivalry battle to capture the continental belt.
The arena fell silent for a extremely emotional homage before the fight as 10 bells tolled in remembrance of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime ended, the silence became a chant of "only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored attire of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was damaged early, heavy swelling appearing under his face as the pair landed powerful shots.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor barely secured the verdict with official scores of 114-114, narrow lead and 115-112, but both fighters were relentless and full of heart, all the qualities their inspiration Hatton represented.
