UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round contest at the boxing arena.
But the challenger found success, landing some telling single shots in a contest where the styles didn't complement each other, with constant grabbing marring the action.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the arena as he was met by disapproval from the spectators.
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 thought the challenger, 31, deserved the win but the British boxer suffered the second setback of his 28-bout professional journey.
The Champion Claims Win in Uneventful Encounter
The fighter's advancement has plateaued in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He began cautiously, with both competitors ready to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a solid defense to narrowly win the more effective rounds.
The crowd's patience decreased amid frequent holding, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by divided decision in a outstanding local rivalry fight to capture the European light-heavyweight championship.
The arena fell silent for a extremely emotional homage before the fight as a bell ceremony rang in honor of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the silence gave way to a chant of "there's only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was knocked down by a left hook squarely on the chin in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured soon, noticeable damage appearing under his face as the fighters landed powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with scoring tallies of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, everything their inspiration the legend embodied.
