UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a fight where the styles never quite clicked, with excessive holding marring the action.
The officials scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the ringside as he was faced disapproval from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the contender endured the second loss of his 28-bout career.
Buatsi Secures Win in Uneventful Affair
Buatsi's progress has plateaued in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to realize his potential - maybe in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Arthur overcame Rea by divided decision in a excellent local rivalry contest to win the European light-heavyweight championship.
The venue fell silent for a profoundly moving homage prior to the bout as ten bells sounded in remembrance of local hero Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the location since the passing of Hatton. As the last bell disappeared, the silence became a chant of "there's just one Ricky Hatton".
The action during the bout equaled the sentiment. Arthur was sent to the canvas by a significant blow directly to the jaw in the early round, rising shakily to his footing on the count of eight.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up early, noticeable damage appearing under his eye as the fighters exchanged powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
Arthur edged the result with official scores of 114-114, close margin and 115-112, but the two athletes were relentless and full of heart, exactly what their inspiration the legend embodied.
