UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the styles didn't complement each other, with frequent clinching spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," Buatsi said in the arena as he was greeted with boos from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the decision but the British boxer suffered the second setback of his 28-bout career.
Buatsi Claims Win in Uneventful Encounter
His career development has slowed in recent times through promotional disputes and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience diminished amid constant clinching, with the challenger slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but several stanzas were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry contest to capture the European light heavyweight belt.
The stadium grew hushed for a extremely emotional memorial before the fight as a bell ceremony sounded in honor of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell disappeared, the silence became a shout of "there's just one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a left hook squarely on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged early, heavy swelling appearing under his eye as the duo exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity hardly diminished over the full distance.
The victor barely secured the decision with judges scorecards of draw, close margin and clearer margin, but both fighters were relentless and courageous, all the qualities their hero the legend embodied.
