UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round contest at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the arena as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th pro success.
Some ringside observers thought Parker, 31, merited the win but the contender suffered the second loss of his 28-match professional journey.
The Champion Earns Triumph in Uneventful Match
Buatsi's progress has slowed in recent years through management issues and long spells of lack of fights.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to take risks in a calculated initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to edge the cleaner periods.
The crowd's patience decreased because of frequent holding, with Parker falling to the floor several times during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a excellent local rivalry fight to secure the continental belt.
The stadium grew hushed for a extremely emotional tribute prior to the bout as 10 bells sounded in honor of the city's native Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the location since Hatton's death. As the last bell disappeared, the silence transitioned to a shout of "only one Ricky Hatton".
The action during the bout matched the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged early, significant bruising forming under his face as the pair exchanged hard punches.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the result with official scores of 114-114, close margin and wider gap, but the two athletes were persistent and full of heart, everything their inspiration Hatton embodied.
