British light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the techniques never quite clicked, with excessive holding marring the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what defines champions? They succeed," the victor commented in the ringside as he was faced negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the decision but the contender endured the second setback of his 28-bout career.
Buatsi Secures Win in Slow Match
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who utilized a protective stance to narrowly win the cleaner periods.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor multiple occasions during grappling.
Parker ended stronger, but multiple periods were hard to judge. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a excellent all-Manchester contest to capture the continental belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as 10 bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the final chime disappeared, the stillness became a roar of "only one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was floored by a powerful punch directly to the face in the early round, standing uncertainly to his position on the eight count.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling forming under his eye as the fighters exchanged hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the result with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and courageous, all the qualities their idol the legend embodied.
