British light heavyweight Joshua Buatsi earned a win yet disappointing start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the styles failed to mesh, with excessive holding disrupting the action.
The officials had it 96-94 to the winner, with the third a even score.
"It wasn't my finest showing but what defines champions? They succeed," the victor said in the ring as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Some ringside observers felt Parker, thirty-one, deserved the victory but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Claims Triumph in Dull Encounter
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers prepared to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who worked behind a tight guard to barely take the more effective periods.
The spectators' acceptance wore thin during regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Contest
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a excellent Manchester vs Manchester fight to secure the European light heavyweight belt.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in honor of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised fight night in the urban center since Hatton's death. As the final chime ended, the stillness gave way to a roar of "there's just one Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was marked up soon, significant bruising forming under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were relentless and courageous, everything their idol the legend stood for.
