UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the styles never quite clicked, with excessive holding marring the contest.
The scoring judges had it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what do champions do? They succeed," the victor said in the ring as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts felt Parker, 31, should have been awarded the decision but the contender endured the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Match
His career development has slowed in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter ready to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the more effective rounds.
The audience's tolerance wore thin during constant clinching, with Parker going down several times during grappling.
Parker finished the stronger, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just one round.
The victor progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the co-main event, Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to win the European light heavyweight belt.
The arena grew hushed for a extremely emotional tribute ahead of the contest as a bell ceremony rang in honor of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's death. As the final chime disappeared, the stillness became a chant of "only one Hatton".
The fighting during the bout equaled the emotion. Arthur was knocked down by a powerful punch squarely on the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was marked up early, significant bruising forming under his eye as the pair exchanged punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the verdict with judges scorecards of 114-114, narrow lead and 115-112, but each competitor were determined and courageous, everything their inspiration Hatton represented.
