UK light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round fight at the Manchester venue.
But Parker found success, delivering effective clean blows in a fight where the styles didn't complement each other, with constant grabbing disrupting the action.
Two judges judged it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They win," Buatsi commented in the arena as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Slow Match
Buatsi's progress has slowed in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with both competitors ready to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who operated with a tight guard to barely take the better stanzas.
The audience's tolerance decreased during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Hatton Memorial Fuels All-Manchester Battle
In the supporting bout, Arthur beat Rea by close verdict in a excellent local rivalry fight to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional tribute ahead of the contest as ten bells tolled in honor of local hero Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the final chime faded, the silence became a shout of "there's only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the initial stage, rising shakily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up quickly, significant bruising appearing under his eye as the fighters exchanged hard punches.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
The victor edged the decision with judges scorecards of even score, narrow lead and 115-112, but both fighters were persistent and courageous, everything their hero Hatton represented.
