UK light-heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective clean blows in a contest where the techniques failed to mesh, with frequent clinching disrupting the fight.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but what do champions do? They prevail," the victor commented in the ring as he was met by disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Dull Affair
His career development has slowed in recent times through promotional disputes and extended periods of lack of fights.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to barely take the more effective stanzas.
The audience's tolerance wore thin during constant clinching, with Parker going down several times during close exchanges.
The underdog ended stronger, but several stanzas were difficult to score. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry fight to win the European light heavyweight championship.
The arena grew hushed for a deeply poignant memorial ahead of the contest as 10 bells tolled in remembrance of the city's native Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the last bell disappeared, the quiet gave way to a roar of "only one Hatton".
The fighting inside the ropes equaled the sentiment. Arthur was floored by a significant blow flush on the jaw in the initial stage, standing uncertainly to his feet on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, Rea - in competitive blue - was injured soon, significant bruising appearing under his face as the pair landed hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the decision with scoring tallies of even score, 115-113 and wider gap, but the two athletes were relentless and courageous, all the qualities their inspiration Hatton stood for.
