British light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close 10-round bout at the Manchester venue.
But Parker had his moments, delivering effective single shots in a fight where the approaches didn't complement each other, with frequent clinching marring the fight.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but what do champions do? They prevail," the victor stated in the arena as he was greeted with negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, deserved the victory but the British boxer experienced the second loss of his 28-fight career.
Buatsi Claims Triumph in Dull Encounter
The fighter's advancement has slowed in the past few 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 recent support.
He opened tentatively, with both competitors prepared to take risks in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who operated with a solid defense to edge the cleaner rounds.
The audience's tolerance wore thin during regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Hatton Memorial Motivates Local Rivalry Fight
In the co-main event, Arthur overcame Rea by divided decision in a outstanding local rivalry contest to secure the continental title.
The venue grew hushed for a profoundly moving memorial before the fight as a bell ceremony sounded in remembrance of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised match card in the location since Hatton's passing. As the final chime disappeared, the quiet became a chant of "there's only one Ricky Hatton".
The fighting during the bout matched the feeling. Arthur was sent to the canvas by a significant blow flush on the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red shorts of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up quickly, heavy swelling appearing under his orbital area as the duo landed powerful shots.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur edged the result with scoring tallies of draw, close margin and 115-112, but each competitor were persistent and brave, everything their hero Hatton represented.
