UK light heavyweight Joshua Buatsi earned a win yet disappointing start to life under fresh promotional backing with a unanimous decision 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 boxing arena.
But Parker had his moments, landing some telling clean blows in a contest where the techniques failed to mesh, with frequent clinching disrupting the contest.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They win," Buatsi said in the ring as he was greeted with boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the victory but the contender suffered the second setback of his 28-fight career.
Buatsi Earns Win in Uneventful Affair
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who worked behind a protective stance to edge the better rounds.
The crowd's patience wore thin because of regular grabbing, with the challenger slipping to the canvas several times during close exchanges.
Parker closed well, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Motivates Local Rivalry Contest
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a terrific all-Manchester battle to win the European light-heavyweight title.
The venue became quiet for a profoundly moving homage before the fight as a bell ceremony rang in honor of local hero Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the silence became a shout of "there's just one Hatton".
The fighting within the ring equaled the sentiment. The eventual winner was knocked down by a powerful punch directly to the face in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was marked up quickly, significant bruising developing under his eye as the fighters exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the pace rarely dropped over the full distance.
The victor edged the verdict with official scores of draw, close margin and 115-112, but both fighters were determined and courageous, all the qualities their inspiration Hatton embodied.
