British light heavyweight Joshua Buatsi made a winning yet underwhelming beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a close ten-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the approaches never quite clicked, with frequent clinching disrupting the contest.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ringside as he was faced boos from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a 20th pro success.
Several boxing experts believed the challenger, 31, merited the victory but the British boxer endured the second setback of his 28-bout professional journey.
The Champion Claims Win in Slow Affair
The fighter's advancement has plateaued in recent years through management issues and long spells of lack of fights.
Once tipped as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance decreased during regular grabbing, with the challenger going down several times during close exchanges.
Parker closed well, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester fight to capture the European light-heavyweight belt.
The stadium fell silent for a deeply poignant tribute prior to the bout as a bell ceremony rang in memory of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound faded, the stillness became a chant of "only one Hatton".
The fighting inside the ropes equaled the feeling. Arthur was sent to the canvas by a significant blow flush on the chin in the early round, getting up unsteadily to his position on the referee's count.
But the traditional red attire of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged early, noticeable damage appearing under his face as the duo exchanged powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the action hardly diminished over the full distance.
The victor barely secured the verdict with official scores of even score, close margin and wider gap, but the two athletes were persistent and courageous, exactly what their idol the legend represented.
