British light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive ten-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling clean blows in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
Two judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor stated in the ring as he was faced boos from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, 31, deserved the victory but the contender experienced the second defeat of his 28-match professional journey.
Buatsi Secures Victory in Slow Affair
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with both competitors willing to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a protective stance to edge the better periods.
The spectators' acceptance wore thin during frequent holding, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light-heavyweight championship.
The stadium fell silent for a profoundly moving tribute before the fight as 10 bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the last bell ended, the quiet transitioned to a roar of "there's just one Hatton".
The action during the bout matched the feeling. Arthur was sent to the canvas by a powerful punch squarely on the chin in the early round, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was damaged quickly, significant bruising developing under his face as the fighters landed powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the decision with judges scorecards of even score, close margin and clearer margin, but the two athletes were relentless and full of heart, all the qualities their idol Hatton represented.
