UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a fight where the approaches never quite clicked, with excessive holding disrupting the contest.
Two judges judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," the victor stated in the arena as he was faced disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Claims Win in Uneventful Encounter
The fighter's advancement has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors ready to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who utilized a protective stance to edge the cleaner periods.
The spectators' acceptance decreased amid regular grabbing, with Parker going down various instances during grappling.
The underdog ended stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester fight to secure the continental belt.
The stadium became quiet for a profoundly moving tribute ahead of the contest as ten bells sounded in memory of Manchester's own Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's death. As the final chime faded, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the early round, rising shakily to his footing on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was marked up early, heavy swelling appearing under his face as the pair landed hard punches.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor edged the result with scoring tallies of draw, 115-113 and 115-112, but both fighters were relentless and courageous, exactly what their inspiration Hatton represented.
