UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a fight where the styles failed to mesh, with excessive holding disrupting the fight.
The officials had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my best showing but what do champions do? They succeed," Buatsi said in the ring as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts believed Parker, 31, merited the victory but the contender endured the second setback of his 28-fight career.
The Champion Claims Triumph in Dull Affair
The fighter's advancement has slowed in recent years through management issues and extended periods of inactivity.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with the two boxers ready to take risks in a tentative opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who operated with a solid defense to narrowly win the more effective periods.
The crowd's patience wore thin during frequent holding, with the challenger slipping to the canvas various instances during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester fight to win the continental championship.
The arena grew hushed for a profoundly moving tribute before the fight as ten bells sounded in honor of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the final chime faded, the quiet transitioned to a shout of "there's only one Hatton".
The action during the bout reflected the feeling. The eventual winner was floored by a powerful punch directly to the jaw in the second round, rising shakily to his position on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his orbital area as the fighters traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
The victor edged the result with official scores of even score, narrow lead and 115-112, but each competitor were determined and brave, exactly what their idol the legend embodied.
