UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a match where the approaches didn't complement each other, with frequent clinching marring the contest.
The officials scored it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They succeed," the victor said in the ring as he was faced negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts believed the challenger, 31, merited the victory but the contender endured the second loss of his 28-fight career.
Buatsi Earns Victory in Uneventful Encounter
His career development has plateaued in recent years through management issues and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with neither fighter willing to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to edge the better rounds.
The spectators' acceptance diminished amid frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still looks steep.
Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to capture the European light-heavyweight belt.
The venue became quiet for a extremely emotional homage prior to the bout as a bell ceremony rang in remembrance of local hero Hatton, who died 46 years old in last month.
It was the premier televised fight night in the urban center since Hatton's passing. As the last bell ended, the quiet gave way to a shout of "there's just one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a left hook directly to the chin in the early round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was damaged quickly, heavy swelling forming under his face as the fighters exchanged hard punches.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur barely secured the verdict with official scores of 114-114, narrow lead and 115-112, but each competitor were persistent and courageous, all the qualities their hero Hatton represented.
