UK light heavyweight Joshua Buatsi made a winning yet disappointing start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a fight where the techniques never quite clicked, with constant grabbing marring the fight.
Two judges had it 96-94 in favor to the winner, with the third a even score.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi commented in the ring as he was met by boos from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the win but the British boxer suffered the second setback of his 28-fight professional journey.
The Champion Claims Win in Dull Encounter
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a protective stance to narrowly win the more effective stanzas.
The audience's tolerance diminished during regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the European light heavyweight championship.
The venue fell silent for a profoundly moving homage before the fight as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised match card in the location since Hatton's death. As the final chime disappeared, the silence became a roar of "only one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was floored by a left hook flush on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged soon, heavy swelling developing under his orbital area as the pair traded powerful shots.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, narrow lead and 115-112, but both fighters were persistent and full of heart, all the qualities their inspiration the legend embodied.
