UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 to the winner, with the final judge a even score.
"It wasn't my best display but how do champions respond? They win," Buatsi stated in the arena as he was faced negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the victory but the British boxer experienced the second loss of his 28-fight professional journey.
The Champion Secures Win in Slow Affair
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to barely take the cleaner rounds.
The audience's tolerance diminished amid regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but many rounds were difficult to score. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the secondary fight, Arthur beat Rea by close verdict in a excellent all-Manchester contest to win the continental championship.
The stadium became quiet for a deeply poignant homage ahead of the contest as a bell ceremony tolled in honor of Manchester's own Hatton, who died 46 years old in recently.
It was the premier televised match card in the urban center since the passing of Hatton. As the last bell faded, the silence transitioned to a roar of "only one Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was knocked down by a left hook flush on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up soon, noticeable damage appearing under his eye as the fighters landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor narrowly won the decision with judges scorecards of even score, close margin and clearer margin, but both fighters were persistent and full of heart, all the qualities their inspiration the legend embodied.
