UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the styles didn't complement each other, with constant grabbing marring the fight.
The officials judged it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers believed Parker, 31, merited the win but the British boxer experienced the second setback of his 28-bout professional journey.
The Champion Earns Triumph in Uneventful Match
The fighter's advancement has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a last chance - under recent support.
He began cautiously, with the two boxers prepared to overcommit in a tentative opening few rounds.
The challenger, 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 fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a protective stance to narrowly win the more effective stanzas.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas several times during grappling.
Parker closed well, but several stanzas were hard to judge. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian champion Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Inspires Local Rivalry Contest
In the secondary fight, Arthur beat Rea by split-decision in a excellent local rivalry battle to capture the continental belt.
The stadium became quiet for a profoundly moving tribute before the fight as ten bells tolled in honor of local hero Hatton, who passed away at age 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the last bell disappeared, the silence became a shout of "only one Hatton".
The competition during the bout equaled the sentiment. Arthur was knocked down by a left hook flush on the face in the initial stage, rising shakily to his feet on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in opposing blue - was marked up early, significant bruising forming under his orbital area as the pair traded powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur narrowly won the decision with official scores of even score, close margin and wider gap, but both fighters were persistent and brave, exactly what their hero Hatton stood for.
