UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful single shots in a fight where the styles never quite clicked, with frequent clinching spoiling the fight.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts believed the challenger, thirty-one, deserved the win but the Derbyshire fighter experienced the second defeat of his 28-bout career.
Buatsi Secures Triumph in Slow Match
His career development has stalled in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who operated with a solid defense to barely take the better periods.
The spectators' acceptance wore thin amid regular grabbing, with the challenger going down various instances during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Arthur defeated Rea by close verdict in a excellent all-Manchester fight to capture the continental belt.
The stadium fell silent for a extremely emotional homage ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died aged 46 in last month.
It was the premier televised fight night in the city since the passing of Hatton. As the last bell faded, the silence became a chant of "only one Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a powerful punch flush on the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored shorts of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising forming under his orbital area as the pair traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur edged the verdict with judges scorecards of draw, narrow lead and clearer margin, but the two athletes were determined and courageous, all the qualities their hero Hatton represented.
