British light-heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive 10-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with constant grabbing marring the contest.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi stated in the arena as he was faced negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts felt Parker, thirty-one, merited the win but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
The Champion Earns Win in Uneventful Match
His career development has stalled in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was participating in his second fight at light heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a protective stance to edge the cleaner periods.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester contest to capture the continental belt.
The stadium fell silent for a profoundly moving memorial ahead of the contest as 10 bells tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the concluding sound ended, the silence gave way to a roar of "there's just one Ricky Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was floored by a left hook flush on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up soon, significant bruising appearing under his face as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur narrowly won the decision with judges scorecards of even score, close margin and wider gap, but both fighters were persistent and full of heart, everything their hero the legend represented.
