UK light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a close ten-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a fight where the techniques never quite clicked, with excessive holding disrupting the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They win," the victor stated in the ringside as he was greeted with boos from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers thought Parker, 31, merited the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Slow Match
Buatsi's progress has slowed in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter willing to overcommit in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the better periods.
The spectators' acceptance decreased during regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Tribute Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur overcame Rea by divided decision in a terrific local rivalry contest to capture the continental belt.
The venue grew hushed for a deeply poignant homage before the fight as ten bells rang in remembrance of local hero Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the last bell disappeared, the stillness became a roar of "there's just one Hatton".
The action during the bout reflected the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the face in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red attire of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured soon, significant bruising appearing under his face as the duo traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and 115-112, but both fighters were relentless and full of heart, exactly what their inspiration Hatton represented.
