British light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a match where the techniques failed to mesh, with frequent clinching marring the action.
The officials judged it 96-94 to the winner, with the third a even score.
"It wasn't my finest display but what defines champions? They win," Buatsi commented in the arena as he was greeted with disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the win but the British boxer endured the second defeat of his 28-fight professional journey.
Buatsi Claims Victory in Slow Match
His career development has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the future of UK 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 be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who worked behind a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance decreased during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester fight to secure the European light-heavyweight title.
The stadium became quiet for a deeply poignant memorial ahead of the contest as ten bells tolled in memory of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the silence gave way to a roar of "there's only one Ricky Hatton".
The competition within the ring equaled the emotion. The eventual winner was knocked down by a left hook flush on the face in the second round, getting up unsteadily to his feet on the eight count.
But the red-colored attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his eye as the duo landed hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor edged the result with scoring tallies of even score, 115-113 and 115-112, but both fighters were relentless and brave, everything their hero Hatton stood for.
