British light heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a close ten-round bout at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the techniques didn't complement each other, with excessive holding spoiling the action.
The officials judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi stated in the ring as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to secure a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the contender suffered the second defeat of his 28-fight career.
Buatsi Claims Triumph in Slow Match
His career development has plateaued in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a protective stance to edge the more effective periods.
The crowd's patience wore thin because of frequent holding, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Although, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a excellent all-Manchester contest to secure the European light heavyweight title.
The stadium fell silent for a profoundly moving homage prior to the bout as ten bells sounded in remembrance of local hero Hatton, who succumbed aged 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the last bell disappeared, the stillness gave way to a roar of "there's just one Hatton".
The competition within the ring matched the emotion. Arthur was knocked down by a significant blow squarely on the face in the second round, rising shakily to his footing on the count of eight.
But the red-colored equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was marked up soon, significant bruising forming under his orbital area as the fighters landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the result with official scores of 114-114, close margin and 115-112, but both fighters were relentless and brave, all the qualities their inspiration Hatton embodied.
