UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the approaches never quite clicked, with frequent clinching marring the contest.
Two judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the arena as he was met by negative reactions from the spectators.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Various analysts believed the challenger, thirty-one, should have been awarded the decision but the British boxer endured the second defeat of his 28-match career.
Buatsi Claims Victory in Slow Match
The fighter's advancement has stalled in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to overcommit 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 mid-fight, was participating in his second bout at the higher weight class.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to narrowly win the better periods.
The spectators' acceptance decreased during frequent holding, with Parker going down various instances during close exchanges.
Parker closed well, but several stanzas were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the co-main event, Lyndon Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester fight to capture the continental championship.
The stadium grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony rang in remembrance of local hero Ricky Hatton, who passed away at age 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a chant of "there's only one Hatton".
The action during the bout equaled the feeling. The eventual winner was knocked down by a significant blow flush on the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the red-colored shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his face as the pair traded hard punches.
Rea, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor edged the result with scoring tallies of 114-114, narrow lead and wider gap, but both fighters were persistent and courageous, all the qualities their idol Hatton embodied.
