British light-heavyweight Joshua Buatsi earned a win yet disappointing start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the approaches never quite clicked, with constant grabbing disrupting the contest.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi said in the ring as he was greeted with boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts believed the challenger, 31, deserved the victory but the British boxer endured the second defeat of his 28-fight career.
Buatsi Secures Win in Slow Encounter
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors willing to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who operated with a protective stance to barely take the better rounds.
The spectators' acceptance wore thin because of frequent holding, with Parker slipping to the canvas various instances during clinches.
The underdog ended stronger, but several stanzas were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Rea by divided decision in a terrific Manchester vs Manchester battle to secure the European light heavyweight title.
The venue grew hushed for a deeply poignant homage ahead of the contest as a bell ceremony sounded in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast 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 competition inside the ropes reflected the emotion. Arthur was floored by a significant blow directly to the face in the initial stage, rising shakily to his feet on the eight count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was marked up soon, noticeable damage forming under his orbital area as the pair traded hard punches.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the result with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were relentless and brave, exactly what their hero the legend embodied.
