British light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a match where the techniques failed to mesh, with excessive holding spoiling the action.
The scoring judges had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi stated in the ringside as he was faced boos from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Secures Triumph in Slow Affair
The fighter's advancement has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter willing to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to edge the better rounds.
The audience's tolerance decreased amid regular grabbing, with the challenger going down various instances during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a terrific all-Manchester contest to win the European light-heavyweight title.
The venue grew hushed for a profoundly moving memorial prior to the bout as a bell ceremony sounded in remembrance of the city's native Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the location since Hatton's death. As the last bell faded, the silence became a roar of "only one Ricky Hatton".
The action inside the ropes matched the sentiment. Arthur was floored by a powerful punch directly to the face in the early round, rising shakily to his position on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was marked up early, significant bruising forming under his orbital area as the fighters exchanged hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with judges scorecards of even score, narrow lead and wider gap, but both fighters were relentless and courageous, all the qualities their inspiration Hatton represented.
