UK light-heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the approaches didn't complement each other, with constant grabbing spoiling the contest.
Two judges had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi commented in the arena as he was faced disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-bout career.
Buatsi Secures Triumph in Slow Match
Buatsi's progress has plateaued in recent years through contract problems and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He started carefully, with neither fighter prepared to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to barely take the cleaner stanzas.
The spectators' acceptance wore thin because of frequent holding, with Parker going down multiple occasions during close exchanges.
The underdog closed well, but many rounds were hard to judge. Although, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to win the European light heavyweight belt.
The stadium became quiet for a extremely emotional homage ahead of the contest as 10 bells rang in remembrance of local hero Hatton, who passed away aged 46 in September.
It was the premier televised boxing event in the location since Hatton's death. As the concluding sound ended, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was floored by a left hook directly to the face in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, significant bruising developing under his face as the duo exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor edged the verdict with official scores of even score, narrow lead and wider gap, but the two athletes were determined and brave, exactly what their hero Hatton embodied.
