British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger had his moments, delivering effective single shots in a match where the styles didn't complement each other, with excessive holding disrupting the contest.
The scoring judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best display but what defines champions? They succeed," the victor said in the arena as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the contender suffered the second setback of his 28-match professional journey.
Buatsi Secures Win in Dull Match
Buatsi's progress has slowed in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter ready to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who utilized a protective stance to barely take the more effective rounds.
The spectators' acceptance wore thin during constant clinching, with the challenger falling to the floor various instances during grappling.
The underdog closed well, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry contest to capture the European light heavyweight belt.
The arena became quiet for a profoundly moving tribute ahead of the contest as ten bells sounded in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the city since Hatton's death. As the concluding sound faded, the quiet became a shout of "there's just one Hatton".
The action inside the ropes matched the emotion. Arthur was sent to the canvas by a significant blow flush on the jaw in the early round, getting up unsteadily to his position on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage forming under his orbital area as the fighters landed powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over 12 rounds.
The victor barely secured the verdict with official scores of draw, close margin and wider gap, but each competitor were persistent and courageous, exactly what their inspiration the legend embodied.
