British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a close 10-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a fight where the approaches failed to mesh, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They prevail," the victor commented in the arena as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Various analysts felt Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second loss of his 28-fight career.
Buatsi Secures Win in Uneventful Encounter
The fighter's advancement has stalled in recent times through contract problems and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers ready to be aggressive in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the more effective periods.
The crowd's patience decreased during constant clinching, with Parker going down various instances during clinches.
The underdog closed well, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a outstanding Manchester vs Manchester fight to capture the European light heavyweight championship.
The venue became quiet for a extremely emotional memorial ahead of the contest as ten bells rang in remembrance of local hero Ricky Hatton, who died aged 46 in September.
It was the premier televised fight night in the urban center since Hatton's death. As the concluding sound disappeared, the stillness gave way to a roar of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. Arthur was knocked down by a significant blow flush on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured early, noticeable damage appearing under his face as the duo exchanged punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of draw, narrow lead and wider gap, but each competitor were persistent and courageous, all the qualities their hero the legend stood for.
