UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the techniques failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They win," Buatsi commented in the arena as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the win but the contender experienced the second loss of his 28-bout career.
The Champion Secures Win in Uneventful Encounter
His career development has slowed in recent times through management issues and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under recent support.
He started carefully, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, 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 bout at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who worked behind a tight guard to edge the more effective periods.
The spectators' acceptance wore thin during constant clinching, with Parker going down multiple occasions during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding local rivalry contest to win the European light heavyweight championship.
The venue became quiet for a profoundly moving homage prior to the bout as 10 bells tolled in memory of the city's native Hatton, who died aged 46 in last month.
It was the first major televised boxing event in the city since Hatton's death. As the last bell ended, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the emotion. Arthur was floored by a significant blow directly to the jaw in the second round, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in rival City blue - was damaged early, significant bruising developing under his face as the duo landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over 12 rounds.
Arthur barely secured the result with official scores of even score, 115-113 and 115-112, but each competitor were persistent and full of heart, all the qualities their hero Hatton represented.
