British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close 10-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective clean blows in a fight where the approaches never quite clicked, with excessive holding spoiling the contest.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what defines champions? They win," the victor commented in the ring as he was met by negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, 31, merited the decision but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Secures Win in Uneventful Match
The fighter's advancement has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the more effective rounds.
The crowd's patience wore thin during regular grabbing, with the challenger slipping to the canvas several times during clinches.
Parker finished the stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Hatton Tribute Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific local rivalry fight to secure the European light heavyweight belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as ten bells sounded in honor of Manchester's own Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the stillness transitioned to a roar of "there's only one Hatton".
The fighting within the ring reflected the emotion. Arthur was sent to the canvas by a powerful punch squarely on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up quickly, heavy swelling forming under his orbital area as the duo traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
The victor edged the result with judges scorecards of 114-114, 115-113 and wider gap, but the two athletes were relentless and courageous, everything their inspiration Hatton represented.
