British light heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a fight where the techniques never quite clicked, with constant grabbing disrupting the contest.
The officials had it 96-94 to Buatsi, with the third a even score.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi commented in the ringside as he was met by boos from the audience.
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.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the contender suffered the second defeat of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Encounter
The fighter's advancement has slowed in the past few years through management issues and long spells of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a calculated opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who worked behind a protective stance to narrowly win the more effective rounds.
The crowd's patience diminished amid constant clinching, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but many rounds were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Arthur beat Rea by split-decision in a terrific all-Manchester contest to capture the European light-heavyweight title.
The stadium grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony sounded in memory of local hero Ricky Hatton, who died 46 years old in last month.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a shout of "there's just one Ricky Hatton".
The action inside the ropes equaled the sentiment. Arthur was knocked down by a left hook directly to the face in the initial stage, rising shakily to his footing on the count of eight.
But the traditional red attire of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up soon, heavy swelling developing under his face as the fighters traded hard punches.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
The victor barely secured the decision with judges scorecards of draw, close margin and 115-112, but each competitor were persistent and full of heart, exactly what their idol Hatton embodied.
