British light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a close 10-round fight at the Manchester venue.
But Parker had his moments, delivering effective single shots in a match where the styles never quite clicked, with frequent clinching disrupting the action.
The officials had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what defines champions? They prevail," the victor said in the arena as he was met by disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers believed the challenger, thirty-one, merited the victory but the contender suffered the second defeat of his 28-fight professional journey.
Buatsi Secures Win in Dull Match
Buatsi's progress has stalled in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who operated with a protective stance to narrowly win the more effective rounds.
The spectators' acceptance diminished during regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Rea by split-decision in a terrific local rivalry contest to secure the European light heavyweight championship.
The arena became quiet for a extremely emotional homage prior to the bout as a bell ceremony tolled in memory of local hero Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the quiet gave way to a chant of "there's only one Ricky Hatton".
The fighting during the bout reflected the sentiment. Arthur was floored by a significant blow squarely on the face in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, noticeable damage developing under his orbital area as the pair landed punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur narrowly won the result with judges scorecards of even score, close margin and clearer margin, but the two athletes were relentless and brave, exactly what their idol the legend represented.
