British light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close 10-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful single shots in a match where the styles never quite clicked, with frequent clinching marring the fight.
Two judges had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my finest display but what do champions do? They prevail," Buatsi said in the arena as he was faced disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the victory but the British boxer experienced the second defeat of his 28-bout career.
Buatsi Secures Triumph in Uneventful Affair
His career development has stalled in recent years through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to realize his potential - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors willing to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a tight guard to narrowly win the more effective periods.
The audience's tolerance decreased during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates All-Manchester Contest
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry contest to capture the European light heavyweight championship.
The stadium fell silent for a extremely emotional homage ahead of the contest as ten bells tolled in memory of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell ended, the stillness became a chant of "there's just one Ricky Hatton".
The action within the ring matched the emotion. Arthur was floored by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was marked up quickly, significant bruising developing under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the decision with official scores of draw, 115-113 and 115-112, but the two athletes were determined and full of heart, everything their hero the legend stood for.
