British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a match where the techniques didn't complement each other, with excessive holding disrupting the fight.
Two judges had it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi commented in the ringside as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the British boxer experienced the second setback of his 28-fight professional journey.
The Champion Earns Victory in Dull Affair
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He started carefully, 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 two years ago after suffering a hand injury mid-fight, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The crowd's patience diminished because of regular grabbing, with the challenger going down several times during clinches.
Parker finished the stronger, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a terrific all-Manchester fight to secure the continental title.
The venue became quiet for a profoundly moving tribute prior to the bout as 10 bells tolled in honor of the city's native Hatton, who succumbed at age 46 in September.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the silence transitioned to a chant of "only one Ricky Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the early round, getting up unsteadily to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was marked up quickly, heavy swelling forming under his face as the duo traded hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur narrowly won the verdict with official scores of draw, close margin and 115-112, but the two athletes were persistent and courageous, exactly what their inspiration the legend stood for.
