British light-heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a contest where the techniques failed to mesh, with excessive holding marring the fight.
Two judges scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest performance but what do champions do? They prevail," the victor stated in the ring as he was met by disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the decision but the contender endured the second loss of his 28-match career.
The Champion Secures Win in Uneventful Affair
His career development has stalled in recent years through management issues and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a protective stance to edge the better periods.
The crowd's patience decreased because of frequent holding, with Parker going down multiple occasions during clinches.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Arthur defeated Rea by divided decision in a terrific local rivalry battle to secure the European light-heavyweight belt.
The stadium became quiet for a profoundly moving homage ahead of the contest as 10 bells tolled in honor of local hero Hatton, who died at age 46 in September.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound ended, the silence transitioned to a chant of "there's only one Hatton".
The action during the bout equaled the feeling. The eventual winner was floored by a left hook flush on the chin in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his face as the duo landed hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
Arthur narrowly won the decision with official scores of draw, narrow lead and clearer margin, but the two athletes were determined and courageous, everything their idol the legend represented.
