British light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a fight where the techniques didn't complement each other, with excessive holding marring the fight.
The officials scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," the victor stated in the ringside as he was greeted with boos from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the contender experienced the second defeat of his 28-match career.
Buatsi Claims Triumph in Slow Affair
Buatsi's progress has plateaued in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a last chance - under fresh management.
He started carefully, with neither fighter willing to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to edge the more effective stanzas.
The audience's tolerance diminished during regular grabbing, with Parker going down several times during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight championship.
The venue fell silent for a deeply poignant tribute ahead of the contest as ten bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the final chime ended, the silence became a chant of "there's only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was knocked down by a powerful punch directly to the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was damaged early, heavy swelling forming under his eye as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
Arthur barely secured the verdict with judges scorecards of even score, 115-113 and 115-112, but both fighters were determined and brave, exactly what their idol the legend stood for.
