British light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round fight at the Manchester venue.
But Parker found success, landing some telling clean blows in a contest where the techniques didn't complement each other, with excessive holding marring the fight.
Two judges scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, merited the win but the British boxer suffered the second setback of his 28-fight professional journey.
Buatsi Claims Victory in Slow Encounter
The fighter's advancement has stalled in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the cleaner periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent local rivalry battle to capture the continental belt.
The stadium grew hushed for a profoundly moving memorial ahead of the contest as 10 bells sounded in honor of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound disappeared, the silence gave way to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes reflected the emotion. The eventual winner was floored by a powerful punch flush on the face in the early round, standing uncertainly to his footing on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was injured quickly, significant bruising appearing under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur barely secured the verdict with judges scorecards of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, everything their hero Hatton embodied.
