UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round fight at the boxing arena.
But the challenger found success, landing some telling single shots in a fight where the techniques didn't complement each other, with frequent clinching disrupting the action.
The scoring judges had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my best display but how do champions respond? They succeed," the victor commented in the ring as he was greeted with boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
The Champion Secures Triumph in Uneventful Affair
The fighter's advancement has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under fresh management.
He began cautiously, with neither fighter willing to overcommit in a calculated early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second fight at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who utilized a solid defense to narrowly win the better rounds.
The spectators' acceptance diminished because of regular grabbing, with the challenger falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Inspires All-Manchester Battle
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester battle to secure the continental title.
The stadium grew hushed for a profoundly moving homage before the fight as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the concluding sound disappeared, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was sent to the canvas by a powerful punch squarely on the face in the early round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged early, noticeable damage appearing under his eye as the pair traded punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action hardly diminished over the full distance.
Arthur edged the result with official scores of even score, close margin and 115-112, but both fighters were determined and brave, exactly what their idol Hatton embodied.
