UK light heavyweight Joshua Buatsi earned a win yet underwhelming start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a match where the approaches never quite clicked, with frequent clinching marring the contest.
The scoring judges had it 96-94 to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but what do champions do? They prevail," Buatsi said in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts felt the challenger, 31, deserved the decision but the contender suffered the second setback of his 28-match professional journey.
The Champion Claims Win in Dull Match
The fighter's advancement has slowed in recent times through management issues and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to be aggressive in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who utilized a tight guard to narrowly win the more effective periods.
The crowd's patience wore thin amid regular grabbing, with Parker slipping to the canvas various instances during clinches.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to win the European light-heavyweight championship.
The venue grew hushed for a profoundly moving homage prior to the bout as 10 bells rang in memory of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the last bell faded, the stillness gave way to a roar of "there's only one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was floored by a left hook directly to the face in the second round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage appearing under his orbital area as the fighters landed powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the decision with scoring tallies of draw, narrow lead and wider gap, but both fighters were persistent and brave, exactly what their inspiration Hatton represented.
