British light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight ten-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the styles didn't complement each other, with constant grabbing disrupting the contest.
The officials judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest performance but what do champions do? They prevail," the victor said in the ringside as he was greeted with boos from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, merited the win but the contender endured the second loss of his 28-bout career.
Buatsi Claims Win in Uneventful Match
The fighter's advancement has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a tentative 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 during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to barely take the cleaner stanzas.
The spectators' acceptance wore thin during constant clinching, with the challenger slipping to the canvas several times during clinches.
Parker closed well, but multiple periods were difficult to score. Although, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Fuels Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by close verdict in a excellent local rivalry contest to capture the European light-heavyweight title.
The venue grew hushed for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in September.
It was the premier televised fight night in the location since Hatton's passing. As the concluding sound faded, the silence gave way to a chant of "there's only one Hatton".
The action inside the ropes matched the emotion. Arthur was floored by a powerful punch squarely on the chin in the early round, rising shakily to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was damaged early, significant bruising developing under his face as the pair exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the result with official scores of draw, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their inspiration Hatton embodied.
