UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round fight at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi said in the arena as he was met by boos from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second loss of his 28-match career.
Buatsi Secures Triumph in Uneventful Encounter
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to take risks in a calculated opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who operated with a protective stance to edge the more effective stanzas.
The crowd's patience diminished during constant clinching, with Parker going down several times during close exchanges.
The underdog closed well, but several stanzas were difficult to score. However, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by divided decision in a excellent all-Manchester fight to secure the European light-heavyweight title.
The arena fell silent for a deeply poignant homage before the fight as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the urban center since the passing of Hatton. As the concluding sound ended, the stillness gave way to a roar of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. Arthur was knocked down by a left hook flush on the jaw in the initial stage, standing uncertainly to his position on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured soon, heavy swelling developing under his orbital area as the duo exchanged hard punches.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action hardly diminished over the full distance.
Arthur barely secured the result with scoring tallies of 114-114, narrow lead and clearer margin, but the two athletes were relentless and full of heart, all the qualities their hero the legend represented.
