UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to life 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 competitive ten-round bout at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding disrupting the fight.
The officials scored it 96-94 to the winner, with the final judge a even score.
"It wasn't my best showing but what defines champions? They prevail," Buatsi said in the arena as he was greeted with disapproval from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt Parker, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
The Champion Earns Win in Dull Affair
Buatsi's progress has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a last chance - under recent support.
He started carefully, with both competitors prepared to overcommit in a calculated initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The spectators' acceptance wore thin amid frequent holding, with the challenger going down various instances during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor advances, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Inspires Manchester Derby Fight
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific local rivalry battle to win the European light-heavyweight championship.
The venue became quiet for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the last bell ended, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was floored by a significant blow directly to the jaw in the second round, rising shakily to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up early, significant bruising appearing under his face as the fighters exchanged hard punches.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the result with scoring tallies of even score, narrow lead and clearer margin, but each competitor were determined and courageous, exactly what their hero Hatton stood for.
