UK light-heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a match where the techniques didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the arena as he was met by negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the British boxer endured the second loss of his 28-match professional journey.
Buatsi Claims Victory in Uneventful Affair
His career development has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a last chance - under fresh management.
He began cautiously, with the two boxers willing to overcommit in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to edge the more effective stanzas.
The crowd's patience diminished during constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a excellent all-Manchester battle to secure the continental championship.
The stadium fell silent for a profoundly moving homage before the fight as ten bells rang in honor of Manchester's own Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime faded, the quiet became a roar of "there's only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the initial stage, getting up unsteadily to his position on the referee's count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising developing under his face as the duo landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the action hardly diminished over twelve rounds.
The victor edged the decision with judges scorecards of even score, 115-113 and wider gap, but both fighters were determined and brave, exactly what their inspiration Hatton stood for.
