UK light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a fight where the approaches didn't complement each other, with constant grabbing spoiling the action.
Two judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They win," the victor commented in the ring as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Various analysts believed Parker, 31, should have been awarded the decision but the contender suffered the second defeat of his 28-match career.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He started carefully, with the two boxers willing to take risks in a calculated early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who operated with a solid defense to edge the more effective rounds.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but many rounds were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the continental belt.
The stadium grew hushed for a extremely emotional tribute before the fight as ten bells sounded in honor of Manchester's own Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime disappeared, the quiet gave way to a chant of "only one Hatton".
The action within the ring reflected the emotion. Arthur was knocked down by a significant blow squarely on the chin in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured quickly, heavy swelling forming under his face as the pair traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, close margin and wider gap, but both fighters were determined and full of heart, everything their idol the legend represented.
