UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a close ten-round bout at the boxing arena.
But the challenger found success, landing some telling single shots in a contest where the techniques failed to mesh, with frequent clinching marring the action.
The officials had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi commented in the arena as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers thought Parker, 31, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Claims Win in Uneventful Affair
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to barely take the cleaner stanzas.
The crowd's patience wore thin during regular grabbing, with Parker slipping to the canvas several times during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. However, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding all-Manchester contest to win the continental title.
The venue grew hushed for a extremely emotional homage prior to the bout as a bell ceremony rang in honor of the city's native Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound faded, the stillness became a roar of "only one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was floored by a significant blow squarely on the jaw in the initial stage, getting up unsteadily to his footing on the referee's count.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, significant bruising forming under his face as the duo traded punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur edged the decision with official scores of even score, close margin and wider gap, but each competitor were persistent and courageous, everything their idol the legend stood for.
