UK light-heavyweight Joshua Buatsi earned a win yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a close ten-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with frequent clinching marring the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They win," Buatsi commented in the arena as he was faced disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Various analysts believed the challenger, 31, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Dull Encounter
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now stands trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a protective stance to barely take the cleaner rounds.
The audience's tolerance decreased amid frequent holding, with Parker going down several times during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to capture the continental title.
The arena fell silent for a extremely emotional homage ahead of the contest as 10 bells sounded in memory of local hero Ricky Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the final chime disappeared, the silence transitioned to a shout of "only one Hatton".
The fighting within the ring matched the emotion. Arthur was floored by a significant blow squarely on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was marked up soon, significant bruising developing under his face as the pair traded powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and full of heart, everything their idol Hatton represented.
