British light heavyweight Joshua Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a competitive ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," the victor said in the arena 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 his previous opponent in February - to claim a 20th career victory.
Some ringside observers thought the challenger, 31, deserved the decision but the contender endured the second setback of his 28-fight career.
The Champion Claims Win in Dull Encounter
The fighter's advancement has stalled in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the future of the British fight scene, he now is positioned trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who utilized a protective stance to barely take the better stanzas.
The spectators' acceptance diminished because of constant clinching, with Parker falling to the floor multiple occasions during clinches.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a excellent local rivalry contest to secure the continental title.
The arena fell silent for a extremely emotional memorial before the fight as 10 bells sounded in memory of Manchester's own Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound faded, the quiet transitioned to a roar of "only one Ricky Hatton".
The action during the bout matched the sentiment. The eventual winner was floored by a powerful punch directly to the chin in the early round, standing uncertainly to his footing on the eight count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, noticeable damage appearing under his eye as the fighters exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur barely secured the decision with scoring tallies of draw, close margin and wider gap, but the two athletes were relentless and full of heart, exactly what their idol the legend stood for.
