British light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive 10-round contest at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a match where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The officials had it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest showing but what defines champions? They win," the victor commented in the arena as he was met by boos from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the British boxer suffered the second loss of his 28-match career.
Buatsi Earns Victory in Dull Affair
Buatsi's progress has stalled in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to achieve expectations - maybe in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to take risks in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to edge the cleaner rounds.
The spectators' acceptance wore thin amid frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but many rounds were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the continental championship.
The arena fell silent for a extremely emotional homage prior to the bout as ten bells tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the concluding sound ended, the silence became a roar of "there's only one Hatton".
The fighting within the ring matched the sentiment. Arthur was knocked down by a left hook flush on the face in the early round, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured early, heavy swelling developing under his orbital area as the pair traded hard punches.
Rea, 27, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, 115-113 and 115-112, but each competitor were relentless and full of heart, all the qualities their idol the legend stood for.
