UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a competitive ten-round contest at the boxing arena.
But Parker found success, connecting with powerful individual punches in a contest where the techniques never quite clicked, with constant grabbing disrupting the action.
The scoring judges judged it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," Buatsi said in the ring as he was met by boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, merited the victory but the British boxer suffered the second loss of his 28-match professional journey.
Buatsi Earns Triumph in Dull Match
The fighter's advancement has plateaued in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers willing to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the more effective rounds.
The audience's tolerance wore thin amid regular grabbing, with the challenger slipping to the canvas various instances during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light heavyweight belt.
The arena fell silent for a extremely emotional homage before the fight as ten bells rang in honor of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the location since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "there's just one Hatton".
The action inside the ropes equaled the feeling. The eventual winner was floored by a powerful punch directly to the jaw in the second round, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, heavy swelling developing under his eye as the pair traded powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with scoring tallies of draw, narrow lead and 115-112, but both fighters were relentless and full of heart, all the qualities their idol the legend represented.
