British light heavyweight Joshua Buatsi earned a win yet disappointing debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the approaches didn't complement each other, with constant grabbing marring the action.
The officials scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi stated in the arena as he was met by boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th career victory.
Some ringside observers felt Parker, 31, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
The Champion Claims Win in Uneventful Match
Buatsi's progress has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to take risks in a tentative early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who utilized a solid defense to edge the cleaner rounds.
The spectators' acceptance diminished amid regular grabbing, with the challenger going down several times during grappling.
The underdog finished the stronger, but many rounds were hard to judge. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight belt.
The stadium grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony sounded in honor of Manchester's own Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime faded, the quiet gave way to a roar of "there's just one Hatton".
The competition during the bout reflected the sentiment. The eventual winner was floored by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was injured soon, heavy swelling developing under his face as the duo landed powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the action seldom decreased over twelve rounds.
The victor edged the result with official scores of 114-114, 115-113 and 115-112, but the two athletes were relentless and full of heart, everything their idol Hatton stood for.
