UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a competitive 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a contest where the techniques failed to mesh, with frequent clinching spoiling the contest.
Two judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the arena as he was greeted with disapproval from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, merited the decision but the Derbyshire fighter experienced the second loss of his 28-fight career.
The Champion Secures Triumph in Dull Affair
His career development has stalled in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a last chance - under fresh management.
He started carefully, with both competitors willing to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the cleaner rounds.
The audience's tolerance diminished during frequent holding, with Parker falling to the floor several times during clinches.
The underdog ended stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The venue grew hushed for a profoundly moving tribute before the fight as 10 bells rang in honor of Manchester's own Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the last bell faded, the quiet gave way to a roar of "only one Hatton".
The action during the bout matched the feeling. The eventual winner was floored by a powerful punch flush on the face in the second round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising developing under his orbital area as the duo exchanged punishing blows.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the decision with judges scorecards of even score, 115-113 and wider gap, but each competitor were determined and full of heart, all the qualities their idol the legend stood for.
