British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round fight at the boxing arena.
But Parker had his moments, delivering effective single shots in a fight where the techniques didn't complement each other, with constant grabbing spoiling the contest.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They win," the victor commented in the ring as he was met by boos from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Various analysts believed Parker, 31, deserved the win but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Earns Triumph in Slow Match
His career development has plateaued in recent years through management issues and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He began cautiously, with neither fighter willing to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to edge the better stanzas.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor multiple occasions during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to win the European light-heavyweight title.
The stadium became quiet for a extremely emotional memorial before the fight as ten bells sounded in memory of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell ended, the silence gave way to a shout of "there's just one Hatton".
The competition during the bout reflected the feeling. The eventual winner was floored by a significant blow directly to the face in the early round, standing uncertainly to his position on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up quickly, noticeable damage developing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the result with judges scorecards of draw, close margin and wider gap, but each competitor were persistent and brave, exactly what their inspiration the legend embodied.
