UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful individual punches in a match where the techniques failed to mesh, with frequent clinching disrupting the fight.
The officials had it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," the victor commented in the ringside as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the British boxer experienced the second defeat of his 28-fight career.
Buatsi Earns Win in Slow Match
Buatsi's progress has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance decreased because of constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Inspires Local Rivalry Battle
In the secondary fight, Arthur defeated Rea by divided decision in a terrific Manchester vs Manchester contest to capture the continental belt.
The venue grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in memory of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime faded, the silence became a roar of "there's only one Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was floored by a significant blow directly to the face in the second round, getting up unsteadily to his position on the eight count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was injured soon, heavy swelling appearing under his face as the duo landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of even score, 115-113 and wider gap, but the two athletes were persistent and courageous, all the qualities their idol the legend stood for.
