UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective individual punches in a match where the styles didn't complement each other, with excessive holding marring the action.
The scoring judges judged it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi stated in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, merited the victory but the contender experienced the second defeat of his 28-fight professional journey.
Buatsi Earns Victory in Dull Affair
Buatsi's progress has stalled in the past few years through contract problems and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to take risks in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who utilized a solid defense to barely take the better stanzas.
The spectators' acceptance wore thin amid regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a outstanding all-Manchester fight to secure the European light-heavyweight belt.
The venue fell silent for a extremely emotional homage ahead of the contest as ten bells rang in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime disappeared, the quiet gave way to a roar of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. Arthur was knocked down by a powerful punch squarely on the face in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up soon, noticeable damage appearing under his eye as the duo landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with official scores of 114-114, 115-113 and wider gap, but both fighters were relentless and brave, exactly what their inspiration the legend embodied.
