UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round contest at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the techniques failed to mesh, with frequent clinching spoiling the fight.
The officials judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," the victor said in the ring as he was faced disapproval from the spectators.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, merited the decision but the contender endured the second loss of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Affair
The fighter's advancement has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers willing to overcommit in a tentative initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the better periods.
The crowd's patience wore thin during regular grabbing, with the challenger going down various instances during grappling.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the secondary fight, Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester battle to capture the continental championship.
The stadium fell silent for a deeply poignant homage prior to the bout as a bell ceremony rang in honor of local hero Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the location since the passing of Hatton. As the last bell disappeared, the silence gave way to a chant of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the jaw in the initial stage, rising shakily to his footing on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured early, noticeable damage forming under his orbital area as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the decision with official scores of even score, close margin and clearer margin, but the two athletes were determined and brave, exactly what their hero the legend embodied.
