UK light heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a match where the techniques failed to mesh, with excessive holding marring the contest.
The officials scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They prevail," the victor said in the arena as he was met by boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts thought Parker, 31, should have been awarded the decision but the British boxer suffered the second loss of his 28-fight career.
Buatsi Earns Triumph in Dull Encounter
His career development has slowed in recent times through management issues and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second bout at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to barely take the better periods.
The crowd's patience diminished because of regular grabbing, with the challenger going down multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Homage Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Rea by split-decision in a outstanding local rivalry fight to win the European light-heavyweight championship.
The venue became quiet for a profoundly moving homage prior to the bout as a bell ceremony rang in remembrance of Manchester's own Hatton, who died 46 years old in September.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound faded, the silence gave way to a shout of "there's only one Ricky Hatton".
The competition during the bout matched the sentiment. Arthur was knocked down by a left hook directly to the face in the initial stage, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured quickly, noticeable damage developing under his orbital area as the pair landed punishing blows.
The challenger, 27, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the result with judges scorecards of even score, narrow lead and wider gap, but both fighters were determined and courageous, all the qualities their inspiration the legend represented.
