British light heavyweight Joshua Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a close ten-round bout at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a fight where the techniques failed to mesh, with constant grabbing disrupting the fight.
The officials had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest display but what defines champions? They win," the victor commented in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, deserved the victory but the British boxer endured the second defeat of his 28-fight professional journey.
The Champion Claims Victory in Slow Match
The fighter's advancement has stalled in recent years through management issues and extended periods of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to barely take the better stanzas.
The spectators' acceptance decreased amid frequent holding, with Parker slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Tribute Motivates Local Rivalry Contest
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester battle to win the European light-heavyweight title.
The venue grew hushed for a deeply poignant memorial prior to the bout as ten bells tolled in honor of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's passing. As the concluding sound faded, the quiet became a chant of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. The eventual winner was knocked down by a significant blow flush on the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was injured soon, significant bruising developing under his orbital area as the fighters traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur narrowly won the decision with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were determined and brave, exactly what their idol Hatton represented.
