UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a close 10-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the approaches didn't complement each other, with constant grabbing marring the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi commented in the arena as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Secures Triumph in Slow Match
The fighter's advancement has slowed in the past few years through management issues and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker going down multiple occasions during clinches.
The underdog closed well, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester battle to secure the European light heavyweight title.
The venue grew hushed for a profoundly moving homage ahead of the contest as 10 bells sounded in memory of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell disappeared, the stillness gave way to a chant of "only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was floored by a significant blow directly to the chin in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was marked up soon, heavy swelling developing under his orbital area as the duo exchanged punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor barely secured the decision with official scores of even score, close margin and 115-112, but the two athletes were determined and courageous, everything their hero the legend represented.
