British light heavyweight Joshua Buatsi made a winning yet disappointing start to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a close ten-round bout at the Manchester venue.
But the challenger found success, delivering effective clean blows in a contest where the approaches never quite clicked, with constant grabbing disrupting the action.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi commented in the ring as he was greeted with disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, merited the decision but the British boxer suffered the second setback of his 28-match career.
Buatsi Earns Triumph in Uneventful Encounter
The fighter's advancement has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to narrowly win the cleaner periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down several times during clinches.
The underdog ended stronger, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to capture the European light-heavyweight championship.
The arena fell silent for a deeply poignant tribute before the fight as a bell ceremony rang in honor of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the urban center since Hatton's death. As the concluding sound ended, the quiet transitioned to a shout of "there's only one Hatton".
The fighting during the bout equaled the emotion. The eventual winner was sent to the canvas by a left hook squarely on the chin in the early round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of Arthur soon advanced again. From the other corner, the opponent - in competitive blue - was marked up quickly, significant bruising appearing under his face as the fighters landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur edged the verdict with official scores of draw, narrow lead and clearer margin, but both fighters were determined and brave, everything their inspiration Hatton represented.
