British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close 10-round bout at the Manchester venue.
But the challenger found success, delivering effective single shots in a match where the techniques failed to mesh, with excessive holding spoiling the fight.
The officials had it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They succeed," the victor stated in the ring as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Earns Victory in Uneventful Match
Buatsi's progress has stalled in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to realize his potential - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective stanzas.
The audience's tolerance wore thin because of frequent holding, with Parker falling to the floor various instances during grappling.
Parker ended stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding local rivalry contest to win the European light heavyweight belt.
The venue fell silent for a deeply poignant homage ahead of the contest as ten bells rang in remembrance of the city's native Hatton, who died 46 years old in last month.
It was the first major televised match card in the location since Hatton's passing. As the last bell faded, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was knocked down by a significant blow directly to the jaw in the early round, getting up unsteadily to his position on the referee's count.
But the red-colored attire of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured early, noticeable damage developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
The victor edged the decision with judges scorecards of 114-114, narrow lead and wider gap, but both fighters were determined and courageous, all the qualities their inspiration the legend stood for.
