British light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the ringside as he was faced disapproval from the crowd.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, 31, deserved the win but the contender experienced the second loss of his 28-bout professional journey.
The Champion Secures Win in Dull Affair
Buatsi's progress has slowed in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who worked behind a protective stance to barely take the cleaner periods.
The crowd's patience diminished because of constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Fuels Local Rivalry Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester battle to secure the European light-heavyweight title.
The arena fell silent for a extremely emotional tribute before the fight as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the urban center since the passing of Hatton. As the last bell ended, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was knocked down by a powerful punch directly to the chin in the second round, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged quickly, significant bruising developing under his face as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
The victor barely secured the result with scoring tallies of draw, 115-113 and 115-112, but the two athletes were relentless and brave, everything their idol the legend represented.
