British light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the approaches didn't complement each other, with frequent clinching disrupting the action.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They succeed," the victor stated in the ringside as he was met by boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, deserved the victory but the British boxer suffered the second loss of his 28-fight career.
Buatsi Earns Victory in Dull Match
His career development has plateaued in recent times through contract problems and extended periods of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter prepared to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who utilized a solid defense to barely take the more effective rounds.
The crowd's patience diminished during frequent holding, with Parker going down multiple occasions during grappling.
Parker closed well, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a outstanding all-Manchester battle to secure the continental title.
The venue fell silent for a deeply poignant homage ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the last bell faded, the stillness became a shout of "there's just one Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a powerful punch directly to the face in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was marked up early, noticeable damage appearing under his face as the pair landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over 12 rounds.
Arthur barely secured the decision with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were persistent and full of heart, everything their inspiration Hatton embodied.
