British light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a contest where the approaches didn't complement each other, with constant grabbing marring the contest.
Two judges had it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but what do champions do? They win," Buatsi commented in the ring as he was faced boos from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Match
His career development has stalled in the past few years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under recent support.
He began cautiously, with both competitors ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for the favorite, who worked behind a solid defense to edge the more effective rounds.
The spectators' acceptance decreased amid regular grabbing, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but many rounds were challenging to assess. However, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Fuels All-Manchester Contest
In the co-main event, Arthur defeated Rea by close verdict in a terrific Manchester vs Manchester battle to win the continental championship.
The arena grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony rang in memory of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound faded, the quiet transitioned to a chant of "there's just one Hatton".
The action during the bout equaled the sentiment. The eventual winner was knocked down by a powerful punch squarely on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up quickly, noticeable damage appearing under his face as the fighters traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were determined and full of heart, all the qualities their idol Hatton represented.
