UK light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches didn't complement each other, with frequent clinching spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi commented in the arena as he was faced negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the victory but the British boxer suffered the second setback of his 28-match career.
Buatsi Secures Win in Uneventful Affair
Buatsi's progress has slowed in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under recent support.
He began cautiously, with neither fighter ready to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second appearance at light-heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a solid defense to barely take the cleaner periods.
The spectators' acceptance decreased during frequent holding, with the challenger falling to the floor multiple occasions during grappling.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Motivates Local Rivalry Battle
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to secure the European light heavyweight title.
The stadium fell silent for a extremely emotional memorial prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast match card in the city since Hatton's passing. As the last bell disappeared, the stillness became a chant of "only one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, standing uncertainly to his position on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was marked up quickly, heavy swelling developing under his face as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
The victor barely secured the decision with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were relentless and brave, exactly what their inspiration the legend represented.
