UK light heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a fight where the techniques never quite clicked, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They win," Buatsi said in the ringside as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts thought the challenger, 31, merited the decision but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Secures Win in Dull Match
Buatsi's progress has slowed in recent years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors willing to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance diminished during regular grabbing, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a outstanding local rivalry fight to secure the European light-heavyweight championship.
The stadium fell silent for a profoundly moving homage ahead of the contest as ten bells rang in memory of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the final chime faded, the silence transitioned to a shout of "there's only one Hatton".
The competition inside the ropes matched the sentiment. Arthur was floored by a powerful punch squarely on the chin in the second round, rising shakily to his feet on the eight count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured quickly, significant bruising appearing under his face as the duo landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the action rarely dropped over twelve rounds.
The victor barely secured the verdict with official scores of draw, narrow lead and wider gap, but both fighters were persistent and full of heart, all the qualities their idol Hatton embodied.
