British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the approaches failed to mesh, with constant grabbing spoiling the fight.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor stated in the ringside as he was faced disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt Parker, 31, merited the decision but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Uneventful Affair
His career development has slowed in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who operated with a tight guard to barely take the more effective periods.
The crowd's patience wore thin during regular grabbing, with the challenger going down several times during clinches.
Parker closed well, but multiple periods were difficult to score. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Fuels Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a outstanding local rivalry contest to secure the European light heavyweight championship.
The stadium grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony sounded in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell ended, the quiet transitioned to a shout of "there's just one Hatton".
The action during the bout equaled the sentiment. Arthur was sent to the canvas by a left hook directly to the jaw in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured early, significant bruising appearing under his orbital area as the duo traded powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the result with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and courageous, exactly what their idol Hatton embodied.
