UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round bout at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a contest where the approaches never quite clicked, with excessive holding marring the fight.
Two judges scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," the victor said in the ring as he was met by negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the victory but the contender endured the second setback of his 28-fight professional journey.
Buatsi Claims Win in Uneventful Match
The fighter's advancement has stalled in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He started carefully, with both competitors ready to overcommit in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the better stanzas.
The crowd's patience decreased during frequent holding, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific local rivalry fight to capture the European light-heavyweight championship.
The stadium grew hushed for a deeply poignant tribute before the fight as ten bells rang in remembrance of local hero Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the city since the passing of Hatton. As the last bell disappeared, the silence gave way to a chant of "there's only one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was floored by a significant blow squarely on the chin in the second round, standing uncertainly to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was damaged early, heavy swelling appearing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur edged the result with judges scorecards of draw, narrow lead and clearer margin, but both fighters were relentless and brave, exactly what their hero Hatton represented.
