UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a close ten-round fight at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a fight where the styles failed to mesh, with frequent clinching disrupting the action.
The officials judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor commented in the ringside as he was faced negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Several boxing experts felt Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Affair
The fighter's advancement has plateaued in recent years through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the better rounds.
The audience's tolerance diminished during regular grabbing, with Parker falling to the floor various instances during grappling.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian champion Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Lyndon Arthur beat Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light heavyweight title.
The stadium became quiet for a profoundly moving tribute before the fight as ten bells rang in remembrance of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the city since Hatton's death. As the last bell disappeared, the silence gave way to a chant of "there's just one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was knocked down by a left hook flush on the face in the initial stage, standing uncertainly to his footing on the count of eight.
But the red-colored equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged quickly, heavy swelling appearing under his face as the pair landed powerful shots.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
The victor edged the verdict with official scores of draw, 115-113 and wider gap, but each competitor were relentless and courageous, everything their inspiration the legend embodied.
