British light heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker had his moments, landing some telling clean blows in a contest where the styles failed to mesh, with excessive holding disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but what do champions do? They succeed," the victor said in the arena as he was met by boos from the audience.
The British fighter got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the win but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
Buatsi Earns Win in Dull Affair
Buatsi's progress has plateaued in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the cleaner periods.
The crowd's patience decreased amid regular grabbing, with the challenger going down several times during clinches.
Parker ended stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light-heavyweight championship.
The venue became quiet for a deeply poignant memorial prior to the bout as ten bells rang in honor of the city's native Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the silence became a shout of "only one Hatton".
The competition during the bout matched the sentiment. Arthur was knocked down by a left hook directly to the face in the initial stage, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, heavy swelling forming under his eye as the pair landed powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur narrowly won the verdict with official scores of even score, narrow lead and wider gap, but the two athletes were persistent and brave, all the qualities their idol the legend stood for.
