British light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close 10-round fight at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the techniques didn't complement each other, with frequent clinching disrupting the contest.
The officials judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi stated in the arena as he was faced boos from the spectators.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the contender experienced the second loss of his 28-bout career.
The Champion Secures Victory in Dull Affair
Buatsi's progress has plateaued in recent times through management issues and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a protective stance to edge the better rounds.
The spectators' acceptance wore thin during constant clinching, with Parker falling to the floor several times during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight belt.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who died at age 46 in September.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime ended, the stillness became a roar of "there's just one Ricky Hatton".
The fighting during the bout reflected the feeling. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged soon, heavy swelling developing under his face as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur narrowly won the result with scoring tallies of 114-114, close margin and clearer margin, but both fighters were relentless and brave, all the qualities their inspiration Hatton represented.
