UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight ten-round contest at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a match where the techniques didn't complement each other, with excessive holding disrupting the fight.
The officials had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They win," Buatsi said in the ringside as he was met by negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Various analysts thought Parker, 31, merited the victory but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Earns Victory in Uneventful Match
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He started carefully, with both competitors prepared to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to narrowly win the better stanzas.
The crowd's patience wore thin during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester contest to capture the European light heavyweight belt.
The arena became quiet for a extremely emotional homage ahead of the contest as 10 bells tolled in honor of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell ended, the quiet transitioned to a chant of "there's just one Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the chin in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his eye as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the result with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and brave, exactly what their idol the legend stood for.
