British light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a contest where the approaches never quite clicked, with constant grabbing spoiling the action.
Two judges had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best display but how do champions respond? They prevail," the victor commented in the ring as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Uneventful Affair
His career development has stalled in recent years through contract problems and long spells of lack of fights.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the cleaner rounds.
The spectators' acceptance wore thin amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester fight to capture the continental title.
The venue grew hushed for a deeply poignant tribute ahead of the contest as ten bells sounded in memory of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the last bell faded, the silence gave way to a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a significant blow directly to the chin in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged quickly, significant bruising developing under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the decision with judges scorecards of 114-114, narrow lead and clearer margin, but both fighters were relentless and brave, everything their inspiration Hatton represented.
