UK light heavyweight Joshua Buatsi made a winning yet disappointing start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with frequent clinching spoiling the fight.
The officials judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They succeed," the victor stated in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
Buatsi Secures Win in Slow Encounter
Buatsi's progress has stalled in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He began cautiously, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the more effective periods.
The spectators' acceptance wore thin during regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Rea by close verdict in a excellent all-Manchester fight to win the continental championship.
The arena became quiet for a profoundly moving tribute prior to the bout as a bell ceremony sounded in honor of local hero Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound faded, the stillness became a shout of "there's just one Hatton".
The action during the bout reflected the sentiment. Arthur was knocked down by a left hook squarely on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured soon, noticeable damage forming under his eye as the fighters landed punishing blows.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
The victor edged the decision with judges scorecards of draw, close margin and 115-112, but both fighters were persistent and courageous, all the qualities their inspiration the legend represented.
