UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a match where the approaches never quite clicked, with constant grabbing marring the action.
Two judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what do champions do? They prevail," the victor stated in the arena as he was faced disapproval from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Various analysts felt Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Earns Victory in Dull Affair
The fighter's advancement has slowed in recent years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a calculated early stages.
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 middle rounds, Parker had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to barely take the cleaner stanzas.
The crowd's patience decreased amid regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
The underdog closed well, but many rounds were challenging to assess. However, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to secure the continental championship.
The arena became quiet for a extremely emotional memorial before the fight as ten bells tolled in remembrance of local hero Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the city since Hatton's death. As the last bell faded, the silence gave way to a chant of "only one Ricky Hatton".
The competition during the bout equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his eye as the duo landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur barely secured the decision with judges scorecards of draw, narrow lead and 115-112, but each competitor were determined and full of heart, exactly what their hero Hatton represented.
