British light-heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a fight where the approaches failed to mesh, with excessive holding marring the action.
Two judges scored it 96-94 to the winner, with the third a even score.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the ring as he was faced disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts felt Parker, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-match professional journey.
The Champion Secures Win in Dull Affair
The fighter's advancement has slowed in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to edge the cleaner stanzas.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor multiple occasions during grappling.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a excellent all-Manchester fight to secure the continental championship.
The venue became quiet for a extremely emotional tribute before the fight as a bell ceremony rang in memory of local hero Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the concluding sound ended, the stillness transitioned to a chant of "there's just one Hatton".
The action within the ring reflected the emotion. Arthur was knocked down by a left hook squarely on the face in the second round, standing uncertainly to his position on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his eye as the pair landed hard punches.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor barely secured the verdict with judges scorecards of even score, narrow lead and 115-112, but the two athletes were determined and brave, all the qualities their inspiration Hatton represented.
