British light heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under fresh promotional backing 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 boxing arena.
But Parker had his moments, landing some telling individual punches in a fight where the approaches never quite clicked, with excessive holding disrupting the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Various analysts thought Parker, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Dull Affair
His career development has slowed in recent times through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to overcommit in a cagey opening few 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 making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the more effective periods.
The spectators' acceptance decreased because of constant clinching, with Parker going down multiple occasions during grappling.
Parker finished the stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Homage Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester fight to secure the continental belt.
The stadium grew hushed for a deeply poignant homage prior to the bout as 10 bells sounded in memory of the city's native Hatton, who succumbed 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's death. As the concluding sound ended, the silence transitioned to a shout of "there's just one Hatton".
The competition within the ring equaled the emotion. Arthur was knocked down by a left hook flush on the face in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was injured soon, significant bruising developing under his eye as the pair traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity hardly diminished over 12 rounds.
The victor edged the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were relentless and brave, all the qualities their inspiration Hatton represented.
