British light-heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a tight ten-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the techniques didn't complement each other, with frequent clinching marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest display but what do champions do? They win," the victor said in the arena as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Earns Win in Dull Encounter
His career development has plateaued in recent times through promotional disputes and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors prepared to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second bout at light heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the cleaner rounds.
The audience's tolerance wore thin amid frequent holding, with Parker going down multiple occasions during grappling.
Parker finished the stronger, but many rounds were challenging to assess. However, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Homage Inspires Manchester Derby Fight
In the co-main event, Arthur overcame Rea by close verdict in a terrific local rivalry fight to secure the European light-heavyweight title.
The stadium became quiet for a extremely emotional homage before the fight as ten bells sounded in memory of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell faded, the quiet transitioned to a shout of "only one Hatton".
The fighting within the ring reflected the feeling. The eventual winner was knocked down by a left hook squarely on the jaw in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured soon, heavy swelling forming under his face as the pair landed punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the decision with scoring tallies of even score, close margin and wider gap, but both fighters were relentless and full of heart, all the qualities their hero the legend embodied.
