UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the approaches didn't complement each other, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," the victor commented in the ring as he was faced boos from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the contender suffered the second setback of his 28-bout career.
The Champion Claims Triumph in Uneventful Affair
The fighter's advancement has stalled in recent years through management issues and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter ready to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the more effective periods.
The audience's tolerance decreased because of constant clinching, with the challenger going down several times during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to secure the European light heavyweight belt.
The venue became quiet for a deeply poignant homage prior to the bout as a bell ceremony rang in memory of local hero Hatton, who died 46 years old in recently.
It was the first major televised match card in the urban center since Hatton's death. As the concluding sound faded, the silence became a chant of "only one Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was knocked down by a left hook squarely on the face in the second round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was damaged soon, noticeable damage developing under his eye as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the decision with official scores of even score, 115-113 and 115-112, but each competitor were persistent and full of heart, all the qualities their idol Hatton represented.
