British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling clean blows in a fight where the styles failed to mesh, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest showing but what do champions do? They win," Buatsi stated in the ringside as he was greeted with negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the British boxer experienced the second loss of his 28-match professional journey.
The Champion Claims Win in Dull Encounter
Buatsi's progress has slowed in the past few years through management issues and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what feels like a last chance - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the better rounds.
The crowd's patience wore thin because of constant clinching, with the challenger falling to the floor several times during close exchanges.
The underdog closed well, but several stanzas were difficult to score. However, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Fight
In the secondary fight, Arthur beat Rea by split-decision in a excellent Manchester vs Manchester contest to secure the European light heavyweight championship.
The arena became quiet for a extremely emotional memorial prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who died aged 46 in recently.
It was the premier televised fight night in the location since Hatton's passing. As the concluding sound faded, the silence became a chant of "there's just one Ricky Hatton".
The fighting during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was damaged early, heavy swelling forming under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the verdict with scoring tallies of even score, 115-113 and 115-112, but the two athletes were persistent and courageous, exactly what their inspiration the legend stood for.
