UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start 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 majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the techniques didn't complement each other, with constant grabbing marring the action.
The scoring judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but what do champions do? They prevail," the victor commented in the arena as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the contender endured the second setback of his 28-fight career.
Buatsi Earns Win in Slow Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the more effective periods.
The crowd's patience wore thin during regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Arthur overcame Rea by close verdict in a terrific local rivalry contest to capture the European light heavyweight belt.
The venue fell silent for a deeply poignant homage prior to the bout as ten bells rang in memory of local hero Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the last bell faded, the silence became a shout of "there's just one Ricky Hatton".
The competition during the bout matched the sentiment. Arthur was knocked down by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling appearing under his eye as the fighters landed hard punches.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the verdict with official scores of draw, narrow lead and clearer margin, but both fighters were determined and brave, everything their idol the legend embodied.
