UK light heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective clean blows in a fight where the approaches failed to mesh, with excessive holding disrupting the action.
The officials had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my greatest performance but how do champions respond? They win," the victor commented in the ring as he was faced boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers thought Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second setback of his 28-match career.
The Champion Claims Triumph in Dull Encounter
The fighter's advancement has slowed in recent years through contract problems and long spells of lack of fights.
Once tipped as the rising talent of UK boxing, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He started carefully, with both competitors ready to be aggressive in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased amid regular grabbing, with Parker falling to the floor several times during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Motivates Manchester Derby Battle
In the co-main event, Arthur overcame Rea by split-decision in a excellent local rivalry contest to secure the European light heavyweight championship.
The stadium grew hushed for a deeply poignant homage prior to the bout as a bell ceremony sounded in honor of local hero Ricky Hatton, who died 46 years old in recently.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the quiet gave way to a chant of "there's just one Hatton".
The competition inside the ropes matched the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the early round, rising shakily to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged quickly, significant bruising appearing under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the result with official scores of draw, 115-113 and clearer margin, but the two athletes were persistent and brave, everything their hero Hatton represented.
