UK light-heavyweight Joshua Buatsi made a winning yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a fight where the techniques didn't complement each other, with frequent clinching disrupting the fight.
The officials had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," the victor stated in the ringside as he was faced disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second setback of his 28-bout professional journey.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has slowed in the past few years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a last chance - under fresh management.
He started carefully, with both competitors willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who utilized a solid defense to barely take the more effective periods.
The audience's tolerance decreased because of frequent holding, with Parker falling to the floor several times during clinches.
Parker closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Arthur beat Rea by split-decision in a terrific local rivalry fight to capture the European light heavyweight title.
The arena grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the silence transitioned to a chant of "there's only one Ricky Hatton".
The competition within the ring matched the emotion. The eventual winner was sent to the canvas by a left hook directly to the jaw in the early round, getting up unsteadily to his feet on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up early, heavy swelling developing under his eye as the duo traded punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the decision with official scores of draw, close margin and 115-112, but the two athletes were determined and courageous, exactly what their idol Hatton represented.
