British light-heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling individual punches in a fight where the techniques didn't complement each other, with frequent clinching disrupting the contest.
The officials had it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They win," Buatsi commented in the ring as he was faced boos from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the win but the British boxer suffered the second setback of his 28-bout career.
The Champion Claims Victory in Uneventful Affair
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under fresh management.
He began cautiously, with both competitors prepared to be aggressive in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who operated with a solid defense to barely take the cleaner periods.
The crowd's patience diminished amid regular grabbing, with the challenger slipping to the canvas various instances during clinches.
Parker closed well, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Arthur beat Rea by divided decision in a terrific Manchester vs Manchester contest to win the European light heavyweight belt.
The arena became quiet for a deeply poignant memorial before the fight as ten bells sounded in honor of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the city since Hatton's passing. As the final chime faded, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The competition within the ring reflected the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the early round, standing uncertainly to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his orbital area as the pair traded powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but both fighters were relentless and brave, all the qualities their idol the legend stood for.
