UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a fight where the approaches never quite clicked, with constant grabbing marring the contest.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi commented in the ringside as he was faced negative reactions from the crowd.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the decision but the contender endured the second loss of his 28-bout professional journey.
The Champion Claims Triumph in Dull Match
His career development has stalled in the past few years through contract problems and long spells of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the cleaner periods.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry battle to capture the European light-heavyweight title.
The venue became quiet for a deeply poignant memorial prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Hatton, who died 46 years old in September.
It was the premier televised fight night in the location since Hatton's death. As the final chime disappeared, the silence became a roar of "there's only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was knocked down by a powerful punch flush on the face in the second round, standing uncertainly to his footing on the referee's count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling appearing under his orbital area as the fighters landed powerful shots.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur barely secured the decision with judges scorecards of even score, close margin and wider gap, but each competitor were relentless and brave, exactly what their inspiration the legend stood for.
