UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close 10-round bout at the Manchester venue.
But the challenger found success, delivering effective single shots in a contest where the approaches failed to mesh, with frequent clinching disrupting the contest.
Two judges scored it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second setback of his 28-fight professional journey.
Buatsi Secures Win in Slow Affair
Buatsi's progress has plateaued in recent times through promotional disputes and considerable time of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with the two boxers willing to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The audience's tolerance wore thin because of frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog closed well, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester contest to win the European light heavyweight championship.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells sounded in honor of local hero Hatton, who died 46 years old in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime ended, the quiet transitioned to a chant of "only one Hatton".
The fighting during the bout equaled the emotion. Arthur was floored by a left hook squarely on the chin in the second round, getting up unsteadily to his feet on the eight count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured soon, noticeable damage forming under his orbital area as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur narrowly won the verdict with official scores of even score, narrow lead and clearer margin, but both fighters were determined and courageous, exactly what their idol the legend stood for.
