UK light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful individual punches in a match where the styles didn't complement each other, with excessive holding marring the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my finest performance but what do champions do? They succeed," the victor stated in the arena as he was met by disapproval from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers thought Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Earns Victory in Dull Encounter
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a calculated initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a solid defense to narrowly win the better stanzas.
The crowd's patience wore thin amid frequent holding, with Parker going down various instances during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the co-main event, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry battle to capture the European light heavyweight title.
The venue became quiet for a profoundly moving tribute ahead of the contest as ten bells tolled in memory of Manchester's own Ricky Hatton, who died 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 faded, the silence gave way to a roar of "there's only one Hatton".
The action during the bout equaled the feeling. The eventual winner was knocked down by a powerful punch directly to the face in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged soon, heavy swelling appearing under his face as the pair landed hard punches.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
Arthur narrowly won the decision with official scores of 114-114, narrow lead and wider gap, but the two athletes were determined and brave, exactly what their idol Hatton represented.
