UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a fight where the techniques failed to mesh, with constant grabbing spoiling the fight.
Two judges scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts thought Parker, 31, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-bout career.
The Champion Secures Win in Dull Affair
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors ready to overcommit in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who utilized a tight guard to narrowly win the better periods.
The crowd's patience decreased amid frequent holding, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Tribute Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Rea by close verdict in a outstanding all-Manchester fight to capture the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage ahead of the contest as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the location since the passing of Hatton. As the concluding sound faded, the silence transitioned to a shout of "there's only one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was knocked down by a left hook directly to the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was damaged quickly, noticeable damage developing under his face as the duo exchanged hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the action seldom decreased over the full distance.
The victor edged the decision with official scores of draw, narrow lead and wider gap, but the two athletes were determined and full of heart, all the qualities their idol Hatton represented.
