UK light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a close 10-round contest at the boxing arena.
But Parker found success, landing some telling individual punches in a fight where the styles failed to mesh, with excessive holding marring the contest.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but what do champions do? They win," the victor stated in the arena as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-bout professional journey.
Buatsi Secures Win in Dull Encounter
Buatsi's progress has stalled in recent years through management issues and long spells of inactivity.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what feels like a last chance - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to edge the better periods.
The spectators' acceptance diminished during constant clinching, with Parker going down several times during grappling.
The underdog closed well, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to secure the European light-heavyweight championship.
The venue fell silent for a profoundly moving memorial prior to the bout as 10 bells sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound faded, the stillness gave way to a shout of "there's only one Ricky Hatton".
The fighting inside the ropes matched the feeling. Arthur was floored by a powerful punch squarely on the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was marked up quickly, noticeable damage forming under his eye as the fighters traded powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, fought fire with fire with stinging uppercuts as the pace rarely dropped over 12 rounds.
The victor barely secured the verdict with official scores of even score, close margin and 115-112, but both fighters were relentless and courageous, everything their idol Hatton embodied.
