UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a contest where the styles didn't complement each other, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They prevail," the victor commented in the ringside as he was met by boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts felt Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Uneventful Affair
The fighter's advancement has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a tentative early stages.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the better rounds.
The audience's tolerance decreased amid frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry contest to win the European light heavyweight title.
The venue became quiet for a extremely emotional tribute prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's passing. As the last bell faded, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the second round, standing uncertainly to his position on the referee's count.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged soon, heavy swelling forming under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor edged the result with official scores of draw, narrow lead and wider gap, but both fighters were relentless and courageous, exactly what their hero the legend embodied.
