British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a match where the styles failed to mesh, with frequent clinching marring the contest.
Two judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the decision but the contender experienced the second defeat of his 28-bout career.
Buatsi Claims Win in Uneventful Encounter
Buatsi's progress has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who utilized a solid defense to narrowly win the cleaner rounds.
The spectators' acceptance wore thin during frequent holding, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the supporting bout, Arthur defeated Rea by split-decision in a outstanding local rivalry battle to secure the European light-heavyweight title.
The venue became quiet for a profoundly moving homage before the fight as a bell ceremony rang in remembrance of Manchester's own Hatton, who died at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime disappeared, the quiet gave way to a shout of "there's only one Hatton".
The action within the ring matched the sentiment. Arthur was floored by a powerful punch directly to the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, significant bruising appearing under his face as the pair exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur barely secured the verdict with scoring tallies of draw, 115-113 and 115-112, but both fighters were relentless and courageous, exactly what their inspiration Hatton represented.
