British light-heavyweight Joshua Buatsi secured a victory yet disappointing start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a match where the approaches didn't complement each other, with constant grabbing disrupting the fight.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," the victor stated in the ringside as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, merited the victory but the British boxer experienced the second defeat of his 28-fight career.
Buatsi Secures Triumph in Slow Encounter
His career development has slowed in the past few years through management issues and considerable time of lack of fights.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under recent support.
He began cautiously, with both competitors willing to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to edge the cleaner rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger falling to the floor several times during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Hatton Homage Inspires All-Manchester Battle
In the supporting bout, Arthur defeated Rea by close verdict in a excellent local rivalry fight to win the continental championship.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in memory of the city's native Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound faded, the quiet became a shout of "there's only one Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was knocked down by a significant blow flush on the jaw in the initial stage, rising shakily to his footing on the eight count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up early, significant bruising appearing under his face as the pair traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the result with judges scorecards of even score, close margin and clearer margin, but both fighters were relentless and full of heart, exactly what their idol the legend stood for.
