British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight 10-round bout at the Manchester venue.
But Parker found success, landing some telling individual punches in a contest where the approaches never quite clicked, with constant grabbing disrupting the fight.
Two judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my best showing but what defines champions? They win," the victor commented in the ring as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the victory but the British boxer suffered the second defeat of his 28-match professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a calculated early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the cleaner periods.
The spectators' acceptance wore thin during constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
Parker closed well, but multiple periods were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the supporting bout, Arthur beat Rea by split-decision in a terrific Manchester vs Manchester fight to secure the continental title.
The arena became quiet for a extremely emotional tribute ahead of the contest as ten bells sounded in memory of the city's native Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the stillness became a shout of "there's only one Hatton".
The competition during the bout equaled the feeling. The eventual winner was sent to the canvas by a left hook squarely on the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red attire of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged early, heavy swelling appearing under his orbital area as the fighters traded powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor edged the decision with scoring tallies of even score, close margin and clearer margin, but both fighters were persistent and courageous, all the qualities their hero the legend represented.
