British light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the approaches failed to mesh, with excessive holding marring the contest.
The officials judged it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but how do champions respond? They succeed," the victor commented in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the British boxer suffered the second setback of his 28-bout career.
Buatsi Earns Victory in Uneventful Affair
His career development has plateaued in recent years through contract problems and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under recent support.
He opened tentatively, with both competitors prepared to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who worked behind a protective stance to barely take the more effective stanzas.
The spectators' acceptance diminished amid regular grabbing, with the challenger going down various instances during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Inspires Manchester Derby Battle
In the supporting bout, Arthur beat Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to secure the continental belt.
The venue became quiet for a deeply poignant homage ahead of the contest as a bell ceremony rang in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the stillness transitioned to a shout of "only one Hatton".
The action during the bout reflected the emotion. The eventual winner was floored by a left hook directly to the chin in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured early, significant bruising developing under his face as the duo landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor barely secured the result with official scores of draw, 115-113 and wider gap, but both fighters were relentless and full of heart, everything their inspiration the legend embodied.
