UK light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the techniques didn't complement each other, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi commented in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers believed Parker, 31, merited the decision but the contender endured the second loss of his 28-fight professional journey.
The Champion Claims Victory in Uneventful Affair
The fighter's advancement has slowed in the past few years through promotional disputes and extended periods of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who operated with a solid defense to barely take the more effective stanzas.
The spectators' acceptance decreased during constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Inspires Local Rivalry Fight
In the supporting bout, Arthur beat Rea by split-decision in a terrific all-Manchester contest to win the European light heavyweight belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as 10 bells tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's death. As the last bell ended, the stillness gave way to a roar of "there's only one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the traditional red attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, heavy swelling developing under his face as the fighters landed powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the action seldom decreased over the full distance.
Arthur edged the verdict with scoring tallies of draw, 115-113 and 115-112, but both fighters were persistent and brave, all the qualities their hero Hatton embodied.
