UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round bout at the Manchester venue.
But Parker had his moments, landing some telling individual punches in a match where the approaches failed to mesh, with excessive holding spoiling the contest.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi said in the ringside as he was met by boos from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Various analysts believed Parker, 31, deserved the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
The Champion Earns Victory in Uneventful Match
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to narrowly win the more effective periods.
The crowd's patience diminished during constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Fuels Local Rivalry Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry fight to capture the continental belt.
The stadium grew hushed for a deeply poignant tribute ahead of the contest as ten bells tolled in remembrance of Manchester's own Hatton, who died at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound ended, the quiet gave way to a shout of "there's only one Ricky Hatton".
The fighting during the bout reflected the emotion. The eventual winner was knocked down by a powerful punch flush on the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon came forward again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling developing under his face as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur edged the decision with official scores of 114-114, close margin and wider gap, but both fighters were persistent and full of heart, all the qualities their idol the legend represented.
