UK light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a fight where the styles didn't complement each other, with frequent clinching marring the action.
Two judges had it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest display but what do champions do? They succeed," the victor said in the ringside as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt Parker, thirty-one, deserved the win but the British boxer suffered the second defeat of his 28-match professional journey.
The Champion Earns Win in Dull Encounter
Buatsi's progress has plateaued in recent years through management issues and long spells of inactivity.
Previously predicted as the future of British boxing, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to narrowly win the cleaner stanzas.
The spectators' acceptance decreased during constant clinching, with the challenger falling to the floor several times during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still appears challenging.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to secure the continental belt.
The venue grew hushed for a deeply poignant homage prior to the bout as 10 bells sounded in honor of Manchester's own Hatton, who passed away 46 years old in September.
It was the premier televised fight night in the city since Hatton's death. As the concluding sound disappeared, the stillness became a chant of "only one Ricky Hatton".
The fighting during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, rising shakily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up quickly, significant bruising developing under his orbital area as the pair traded punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur edged the decision with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were persistent and courageous, everything their inspiration Hatton stood for.
