British light-heavyweight Joshua Buatsi made a winning yet disappointing debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a match where the styles never quite clicked, with constant grabbing disrupting the contest.
The officials had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi said in the ring as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts believed Parker, thirty-one, merited the victory but the Derbyshire fighter endured the second defeat of his 28-fight professional journey.
Buatsi Earns Triumph in Dull Match
The fighter's advancement has stalled in recent times through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He began cautiously, with the two boxers willing to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who operated with a protective stance to barely take the more effective rounds.
The crowd's patience decreased because of constant clinching, with Parker falling to the floor several times during close exchanges.
Parker closed well, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester fight to win the continental title.
The stadium became quiet for a profoundly moving tribute prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound faded, the quiet became a roar of "only one Hatton".
The fighting inside the ropes equaled the feeling. Arthur was floored by a powerful punch squarely on the chin in the second round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up early, heavy swelling appearing under his face as the pair traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur barely secured the result with official scores of even score, narrow lead and 115-112, but the two athletes were determined and full of heart, exactly what their inspiration the legend embodied.
