UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the styles never quite clicked, with constant grabbing marring the fight.
The officials had it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but what do champions do? They prevail," the victor commented in the ring as he was met by disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers felt Parker, 31, merited the win but the British boxer experienced the second loss of his 28-fight career.
The Champion Earns Win in Slow Match
His career development has plateaued in recent years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers willing to take risks in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who worked behind a tight guard to narrowly win the better rounds.
The crowd's patience wore thin because of frequent holding, with Parker going down various instances during clinches.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a excellent local rivalry fight to secure the European light heavyweight title.
The arena became quiet for a deeply poignant memorial prior to the bout as 10 bells tolled in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime disappeared, the silence became a chant of "there's just one Hatton".
The action during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow squarely on the face in the initial stage, rising shakily to his feet on the eight count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage appearing under his orbital area as the fighters traded punishing blows.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the decision with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and brave, everything their inspiration Hatton stood for.
