UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a tight ten-round fight at the boxing arena.
But the challenger landed significant shots, delivering effective clean blows in a match where the styles didn't complement each other, with constant grabbing spoiling the fight.
The scoring judges had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi stated in the ring as he was met by disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, deserved the win but the contender endured the second defeat of his 28-match professional journey.
The Champion Earns Win in Dull Match
The fighter's advancement has stalled in recent years through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to barely take the better rounds.
The crowd's patience wore thin amid frequent holding, with the challenger going down various instances during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry battle to capture the continental championship.
The arena became quiet for a deeply poignant memorial before the fight as ten bells rang in honor of the city's native Hatton, who passed away at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound disappeared, the stillness gave way to a chant of "there's only one Hatton".
The action within the ring equaled the emotion. The eventual winner was floored by a powerful punch directly to the jaw in the initial stage, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up early, noticeable damage appearing under his eye as the fighters traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor edged the verdict with official scores of even score, 115-113 and 115-112, but each competitor were persistent and brave, all the qualities their idol Hatton embodied.
