UK light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker found success, landing some telling individual punches in a fight where the approaches didn't complement each other, with frequent clinching spoiling the fight.
Two judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best display but how do champions respond? They win," the victor commented in the arena as he was faced negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, 31, should have been awarded the win but the contender endured the second setback of his 28-fight professional journey.
Buatsi Earns Win in Dull Encounter
His career development has slowed in recent times through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a last chance - under new promotional backing.
He started carefully, with neither fighter ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who worked behind a protective stance to edge the cleaner stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
The underdog closed well, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester contest to capture the continental title.
The arena grew hushed for a profoundly moving homage prior to the bout as a bell ceremony tolled in memory of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the final chime disappeared, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The competition inside the ropes reflected the feeling. Arthur was floored by a left hook flush on the jaw in the early round, standing uncertainly to his feet on the eight count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was marked up quickly, significant bruising forming under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the verdict with official scores of draw, narrow lead and clearer margin, but the two athletes were determined and brave, all the qualities their idol Hatton embodied.
