UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a match where the approaches never quite clicked, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi said in the arena as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, should have been awarded the decision but the contender endured the second defeat of his 28-fight career.
The Champion Claims Victory in Dull Encounter
His career development has slowed in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with the two boxers ready to take risks in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the more effective stanzas.
The spectators' acceptance diminished amid constant clinching, with the challenger falling to the floor several times during grappling.
The underdog closed well, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester fight to win the European light-heavyweight belt.
The arena fell silent for a deeply poignant tribute prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the final chime ended, the stillness gave way to a chant of "there's only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was knocked down by a powerful punch squarely on the chin in the initial stage, standing uncertainly to his footing on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged early, significant bruising appearing under his eye as the duo landed punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the result with judges scorecards of draw, narrow lead and 115-112, but each competitor were relentless and brave, exactly what their idol Hatton embodied.
