UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a fight where the techniques never quite clicked, with excessive holding disrupting the fight.
Two judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best performance but what do champions do? They win," the victor stated in the ring as he was met by boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought Parker, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Earns Victory in Dull Encounter
The fighter's advancement has plateaued in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who worked behind a solid defense to narrowly win the more effective rounds.
The audience's tolerance diminished during frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the continental belt.
The stadium became quiet for a profoundly moving tribute prior to the bout as 10 bells rang in memory of the city's native Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime ended, the stillness became a roar of "there's just one Hatton".
The action within the ring equaled the sentiment. Arthur was floored by a powerful punch squarely on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling forming under his face as the duo landed hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the decision with official scores of even score, narrow lead and 115-112, but the two athletes were persistent and full of heart, all the qualities their inspiration the legend embodied.
