British light heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best display but what defines champions? They win," the victor commented in the arena as he was met by negative reactions from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the victory but the British boxer suffered the second setback of his 28-bout professional journey.
Buatsi Claims Win in Dull Match
His career development has plateaued in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with the two boxers prepared to overcommit in a cagey opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to narrowly win the cleaner rounds.
The crowd's patience wore thin during regular grabbing, with the challenger going down various instances during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent all-Manchester contest to secure the continental title.
The venue grew hushed for a profoundly moving homage prior to the bout as ten bells rang in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the city since Hatton's death. As the last bell faded, the silence gave way to a chant of "there's only one Hatton".
The competition during the bout matched the feeling. Arthur was floored by a left hook squarely on the jaw in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up early, heavy swelling appearing under his eye as the fighters traded powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the result with judges scorecards of 114-114, 115-113 and wider gap, but each competitor were relentless and full of heart, everything their hero Hatton stood for.
