UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round bout at the boxing arena.
But Parker had his moments, delivering effective single shots in a match where the styles didn't complement each other, with frequent clinching disrupting the contest.
The officials scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They win," Buatsi commented in the arena as he was met by boos from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the contender endured the second setback of his 28-bout professional journey.
Buatsi Claims Victory in Slow Encounter
His career development has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now finds himself trying to achieve expectations - possibly 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 cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who worked behind a tight guard to barely take the cleaner periods.
The audience's tolerance wore thin during regular grabbing, with Parker going down various instances during clinches.
Parker finished the stronger, but multiple periods were hard to judge. Although, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Inspires Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Rea by split-decision in a outstanding all-Manchester battle to capture the continental championship.
The arena grew hushed for a extremely emotional tribute before the fight as a bell ceremony tolled in memory of the city's native Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the quiet gave way to a shout of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was floored by a left hook squarely on the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red shorts of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was damaged soon, significant bruising appearing under his eye as the duo landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of even score, close margin and 115-112, but the two athletes were relentless and full of heart, everything their inspiration the legend embodied.
