UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close ten-round fight at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the styles never quite clicked, with frequent clinching spoiling the contest.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They win," the victor said in the ringside as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought Parker, 31, merited the decision but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Secures Triumph in Uneventful Affair
Buatsi's progress has stalled in the past few years through management issues and extended periods of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the better rounds.
The audience's tolerance diminished during frequent holding, with Parker going down several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Rea by divided decision in a excellent local rivalry battle to secure the European light heavyweight championship.
The venue grew hushed for a profoundly moving homage ahead of the contest as 10 bells rang in memory of local hero Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell disappeared, the quiet became a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the emotion. Arthur was sent to the canvas by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage forming under his face as the duo traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were determined and full of heart, everything their inspiration Hatton represented.
