UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi commented in the ring as he was met by boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Secures Win in Slow Encounter
His career development has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a calculated opening few rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to edge the better rounds.
The spectators' acceptance wore thin amid constant clinching, with Parker going down various instances during clinches.
Parker finished the stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester battle to win the continental belt.
The venue fell silent for a profoundly moving memorial before the fight as ten bells rang in memory of local hero Ricky Hatton, who died 46 years old in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the final chime disappeared, the silence transitioned to a chant of "only one Hatton".
The action during the bout reflected the sentiment. Arthur was knocked down by a powerful punch flush on the face in the early round, rising shakily to his feet on the eight count.
But the traditional red shorts of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage appearing under his eye as the duo exchanged punishing blows.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over the full distance.
The victor barely secured the decision with judges scorecards of draw, close margin and clearer margin, but the two athletes were relentless and courageous, everything their idol Hatton stood for.
