British light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a contest where the approaches didn't complement each other, with frequent clinching disrupting the contest.
Two judges scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor said in the arena as he was met by negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts thought Parker, thirty-one, merited the win but the British boxer experienced the second loss of his 28-match professional journey.
Buatsi Earns Victory in Dull Match
His career development has plateaued in recent times through management issues and long spells of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who worked behind a protective stance to edge the more effective stanzas.
The spectators' acceptance decreased because of regular grabbing, with the challenger going down various instances during clinches.
Parker closed well, but many rounds were challenging to assess. However, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester battle to win the continental title.
The stadium grew hushed for a profoundly moving homage before the fight as 10 bells rang in remembrance of the city's native Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound disappeared, the stillness gave way to a roar of "there's only one Hatton".
The competition within the ring matched the sentiment. The eventual winner was knocked down by a powerful punch squarely on the jaw in the early round, rising shakily to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling forming under his face as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, 115-113 and 115-112, but the two athletes were relentless and full of heart, all the qualities their hero the legend stood for.
