British light heavyweight Joshua Buatsi secured a victory yet disappointing 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 majority decision in a competitive ten-round contest at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a fight where the styles didn't complement each other, with frequent clinching disrupting the fight.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They succeed," the victor stated in the arena as he was met by boos from the crowd.
The Londoner got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the decision but the British boxer endured the second setback of his 28-fight career.
Buatsi Claims Victory in Dull Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with neither fighter willing to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The audience's tolerance wore thin during frequent holding, with Parker going down multiple occasions during clinches.
Parker closed well, but several stanzas were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Fuels All-Manchester Battle
In the supporting bout, Arthur overcame Rea by close verdict in a terrific local rivalry battle to capture the European light-heavyweight belt.
The arena fell silent for a deeply poignant tribute before the fight as ten bells rang in memory of the city's native Ricky Hatton, who died at age 46 in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the final chime faded, the silence transitioned to a chant of "there's only one Hatton".
The competition during the bout matched the feeling. Arthur was sent to the canvas by a left hook directly to the chin in the early round, rising shakily to his feet on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged soon, noticeable damage forming under his orbital area as the pair traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor edged the result with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were persistent and courageous, all the qualities their hero Hatton embodied.
