UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a match where the approaches never quite clicked, with constant grabbing marring the action.
The officials judged it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They succeed," Buatsi stated in the ringside as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the victory but the contender experienced the second loss of his 28-bout professional journey.
The Champion Earns Victory in Dull Affair
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He opened tentatively, with both competitors willing to overcommit in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to edge the better stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the continental championship.
The arena became quiet for a deeply poignant homage ahead of the contest as ten bells tolled in honor of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the urban center since Hatton's death. As the final chime ended, the stillness gave way to a roar of "there's only one Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was marked up soon, noticeable damage developing under his face as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor narrowly won the result with scoring tallies of 114-114, close margin and clearer margin, but both fighters were relentless and courageous, everything their inspiration the legend represented.
