UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight 10-round contest at the Manchester venue.
But Parker found success, delivering effective individual punches in a fight where the styles never quite clicked, with excessive holding marring the contest.
The officials judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi stated in the ringside as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts believed Parker, 31, should have been awarded the win but the contender endured the second loss of his 28-fight career.
Buatsi Claims Triumph in Dull Match
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers ready to take risks 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 bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who worked behind a protective stance to narrowly win the better rounds.
The audience's tolerance diminished during constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian champion Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Hatton Homage Inspires Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific all-Manchester contest to secure the continental belt.
The stadium fell silent for a profoundly moving tribute before the fight as a bell ceremony sounded in honor of Manchester's own Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the city since Hatton's passing. As the final chime disappeared, the stillness became a shout of "only one Ricky Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was floored by a left hook directly to the chin in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged early, heavy swelling developing under his eye as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the verdict with judges scorecards of draw, close margin and 115-112, but each competitor were determined and full of heart, everything their inspiration the legend represented.
