UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the styles didn't complement each other, with excessive holding disrupting the action.
The officials scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They win," the victor commented in the ringside as he was greeted with boos from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the win but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
The Champion Claims Win in Uneventful Encounter
His career development has slowed in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who operated with a solid defense to barely take the more effective stanzas.
The crowd's patience decreased during constant clinching, with Parker going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Inspires Manchester Derby Contest
In the secondary fight, Arthur beat Rea by split-decision in a excellent all-Manchester fight to secure the European light heavyweight title.
The venue became quiet for a profoundly moving memorial ahead of the contest as a bell ceremony tolled in remembrance of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the location since the passing of Hatton. As the final chime faded, the stillness became a roar of "there's just one Hatton".
The action within the ring matched the sentiment. The eventual winner was sent to the canvas by a left hook flush on the face in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged soon, significant bruising appearing under his face as the fighters exchanged powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, 115-113 and 115-112, but each competitor were relentless and brave, all the qualities their hero Hatton represented.
