British light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my finest display but what do champions do? They win," the victor stated in the arena as he was met by disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers felt the challenger, 31, deserved the win but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Slow Affair
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers ready to take risks in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who operated with a solid defense to edge the cleaner periods.
The crowd's patience decreased because of regular grabbing, with the challenger going down multiple occasions during clinches.
Parker closed well, but many rounds were hard to judge. However, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester contest to secure the continental championship.
The venue became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony sounded in memory of local hero Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime ended, the silence became a chant of "there's just one Ricky Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was floored by a left hook squarely on the face in the second round, rising shakily to his footing on the eight count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage forming under his face as the fighters landed powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over the full distance.
The victor narrowly won the decision with official scores of even score, 115-113 and wider gap, but both fighters were persistent and full of heart, all the qualities their hero the legend stood for.
