British light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling individual punches in a contest where the approaches failed to mesh, with constant grabbing disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but what do champions do? They succeed," Buatsi stated in the ringside as he was met by boos from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, 31, merited the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Secures Victory in Uneventful Match
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - perhaps in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to narrowly win the more effective rounds.
The crowd's patience diminished because of frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Inspires All-Manchester Battle
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a deeply poignant homage before the fight as a bell ceremony rang in honor of the city's native Hatton, who succumbed 46 years old in September.
It was the premier televised match card in the location since Hatton's passing. As the concluding sound faded, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The fighting during the bout equaled the emotion. The eventual winner was knocked down by a powerful punch squarely on the face in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage forming under his orbital area as the duo traded powerful shots.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur barely secured the decision with official scores of draw, narrow lead and clearer margin, but both fighters were persistent and courageous, all the qualities their hero Hatton embodied.
