UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a match where the techniques didn't complement each other, with constant grabbing marring the contest.
The officials had it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ring as he was greeted with boos from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the win but the contender suffered the second loss of his 28-bout professional journey.
The Champion Claims Triumph in Uneventful Match
His career development has stalled in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He opened tentatively, with both competitors ready to take risks in a tentative opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was making just his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who utilized a solid defense to barely take the more effective rounds.
The spectators' acceptance wore thin during regular grabbing, with Parker slipping to the canvas several times during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a terrific all-Manchester fight to capture the European light heavyweight championship.
The stadium grew hushed for a profoundly moving tribute prior to the bout as 10 bells rang in honor of Manchester's own Hatton, who died aged 46 in recently.
It was the first major televised fight night in the location since Hatton's death. As the last bell faded, the stillness became a chant of "only one Hatton".
The fighting within the ring reflected the sentiment. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was marked up quickly, noticeable damage forming under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the decision with judges scorecards of draw, 115-113 and wider gap, but both fighters were persistent and brave, exactly what their inspiration Hatton embodied.
