UK light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles didn't complement each other, with frequent clinching spoiling the contest.
Two judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi stated in the arena as he was faced boos from the spectators.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Various analysts believed Parker, thirty-one, deserved the win but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Earns Victory in Uneventful Match
The fighter's advancement has plateaued in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He started carefully, with the two boxers prepared to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to edge the cleaner rounds.
The audience's tolerance diminished during regular grabbing, with the challenger falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Fuels Local Rivalry Battle
In the secondary fight, Arthur overcame Rea by close verdict in a excellent all-Manchester fight to capture the European light heavyweight belt.
The arena became quiet for a profoundly moving homage ahead of the contest as 10 bells sounded in memory of local hero Hatton, who died aged 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime ended, the silence transitioned to a shout of "only one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the early round, standing uncertainly to his feet on the eight count.
But the red-colored equipment of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling appearing under his orbital area as the duo exchanged hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of draw, close margin and 115-112, but both fighters were persistent and brave, exactly what their idol Hatton embodied.
