British light heavyweight Joshua Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger found success, delivering effective single shots in a match where the styles didn't complement each other, with excessive holding disrupting the fight.
Two judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but what defines champions? They prevail," Buatsi stated in the arena as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, 31, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Earns Win in Uneventful Match
Buatsi's progress has slowed in the past few years through management issues and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers prepared to take risks in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for Buatsi, who utilized a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance decreased because of constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but several stanzas were difficult to score. However, ex-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 Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester contest to secure the European light heavyweight belt.
The arena fell silent for a profoundly moving homage ahead of the contest as a bell ceremony sounded in memory of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the location since Hatton's passing. As the concluding sound faded, the silence transitioned to a shout of "there's just one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the initial stage, rising shakily to his position on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was injured early, heavy swelling forming under his orbital area as the pair traded hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the result with official scores of even score, 115-113 and 115-112, but both fighters were relentless and courageous, everything their inspiration Hatton embodied.
