British light-heavyweight Joshua Buatsi earned a win yet disappointing start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a fight where the styles didn't complement each other, with excessive holding spoiling the action.
Two judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," the victor commented in the ring as he was faced boos from the crowd.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the win but the Derbyshire fighter experienced the second loss of his 28-fight professional journey.
Buatsi Earns Victory in Slow Affair
His career development has slowed in recent times through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who worked behind a solid defense to barely take the more effective rounds.
The spectators' acceptance decreased during regular grabbing, with Parker going down multiple occasions during close exchanges.
The underdog closed well, but many rounds were difficult to score. However, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the continental belt.
The arena fell silent for a deeply poignant memorial prior to the bout as ten bells rang in remembrance of local hero Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the final chime disappeared, the silence transitioned to a shout of "there's just one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up quickly, significant bruising appearing under his orbital area as the duo exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the decision with official scores of even score, close margin and 115-112, but each competitor were persistent and courageous, exactly what their idol Hatton represented.
