UK light heavyweight Joshua Buatsi made a winning yet underwhelming start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling single shots in a contest where the techniques failed to mesh, with constant grabbing disrupting the action.
Two judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my best performance but what do champions do? They win," Buatsi stated in the arena as he was greeted with boos from the spectators.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, 31, merited the victory but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Dull Encounter
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to edge the cleaner periods.
The spectators' acceptance diminished amid constant clinching, with the challenger falling to the floor multiple occasions during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Battle
In the secondary fight, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light-heavyweight title.
The arena grew hushed for a extremely emotional homage ahead of the contest as 10 bells sounded in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell ended, the silence transitioned to a roar of "there's just one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was sent to the canvas by a left hook flush on the chin in the second round, rising shakily to his footing on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up early, noticeable damage forming under his face as the pair traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the result with judges scorecards of draw, close margin and 115-112, but each competitor were persistent and courageous, everything their idol the legend represented.
