UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a close 10-round contest at the Manchester venue.
But the challenger found success, landing some telling single shots in a contest where the approaches failed to mesh, with frequent clinching disrupting the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the ring as he was met by disapproval from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts felt the challenger, 31, deserved the decision but the contender suffered the second loss of his 28-match career.
Buatsi Secures Triumph in Dull Match
His career development has plateaued in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated opening few 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 bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a solid defense to narrowly win the better rounds.
The spectators' acceptance decreased amid frequent holding, with Parker slipping to the canvas various instances during grappling.
The underdog closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor moves on, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Homage Motivates Local Rivalry Contest
In the supporting bout, Arthur overcame Rea by split-decision in a outstanding local rivalry battle to secure the continental title.
The arena fell silent for a profoundly moving homage prior to the bout as 10 bells sounded in honor of the city's native Ricky Hatton, who died aged 46 in September.
It was the first major televised match card in the city since the passing of Hatton. As the final chime ended, the quiet gave way to a shout of "only one Hatton".
The fighting within the ring matched the emotion. The eventual winner was floored by a left hook squarely on the face in the second round, rising shakily to his position on the referee's count.
But the traditional red attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was damaged soon, significant bruising forming under his face as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the action hardly diminished over the full distance.
Arthur edged the result with judges scorecards of draw, 115-113 and clearer margin, but each competitor were persistent and full of heart, everything their inspiration Hatton stood for.
