UK light-heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a contest where the styles never quite clicked, with frequent clinching disrupting the action.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They prevail," Buatsi stated in the ring as he was faced disapproval 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 twentieth professional win.
Several boxing experts believed Parker, 31, merited the victory but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Claims Victory in Dull Affair
Buatsi's progress has stalled in recent years through management issues and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under new promotional backing.
He opened tentatively, with the two boxers ready to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat 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 fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the cleaner periods.
The spectators' acceptance wore thin because of regular grabbing, with the challenger going down various instances during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a terrific local rivalry contest to secure the European light heavyweight championship.
The stadium fell silent for a extremely emotional tribute before the fight as 10 bells tolled in honor of Manchester's own Hatton, who died at age 46 in September.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound ended, the stillness gave way to a shout of "only one Hatton".
The fighting during the bout reflected the feeling. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, rising shakily to his position on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was injured quickly, significant bruising developing under his face as the duo exchanged hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the intensity hardly diminished over the full distance.
The victor edged the decision with judges scorecards of 114-114, 115-113 and clearer margin, but both fighters were persistent and full of heart, all the qualities their hero the legend represented.
