UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a tight 10-round bout at the boxing arena.
But the challenger found success, landing some telling clean blows in a contest where the styles never quite clicked, with excessive holding marring the action.
Two judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They prevail," the victor said in the ring as he was faced boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-match career.
Buatsi Claims Triumph in Uneventful Match
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a tight guard to edge the better periods.
The audience's tolerance diminished during regular grabbing, with the challenger going down multiple occasions during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester battle to win the European light heavyweight championship.
The venue became quiet for a deeply poignant tribute prior to the bout as ten bells tolled in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a roar of "there's only one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a left hook flush on the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was damaged soon, noticeable damage appearing under his face as the duo traded powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
The victor edged the result with judges scorecards of even score, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their hero Hatton represented.
