UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round contest at the Manchester venue.
But Parker landed significant shots, landing some telling single shots in a contest where the techniques failed to mesh, with frequent clinching disrupting the fight.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi said in the ringside as he was met by negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Some ringside observers believed the challenger, thirty-one, merited the victory but the contender suffered the second setback of his 28-fight career.
Buatsi Secures Triumph in Uneventful Affair
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The spectators' acceptance diminished amid constant clinching, with Parker falling to the floor multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the secondary fight, Arthur beat Rea by split-decision in a outstanding all-Manchester contest to win the continental title.
The arena grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the urban center since Hatton's death. As the concluding sound ended, the quiet became a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the sentiment. The eventual winner was floored by a significant blow directly to the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was damaged soon, significant bruising developing under his eye as the fighters exchanged powerful shots.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the decision with scoring tallies of 114-114, narrow lead and wider gap, but both fighters were relentless and full of heart, everything their inspiration Hatton embodied.
