UK light heavyweight Joshua Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a tight ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a match where the approaches failed to mesh, with frequent clinching disrupting the action.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," the victor stated in the ringside as he was faced disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-fight career.
Buatsi Secures Triumph in Slow Match
His career development has stalled in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the better rounds.
The crowd's patience wore thin during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but several stanzas were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a outstanding local rivalry battle to capture the continental title.
The venue became quiet for a deeply poignant tribute prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the urban center since the passing of Hatton. As the last bell ended, the stillness transitioned to a roar of "only one Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a left hook flush on the chin in the early round, getting up unsteadily to his footing on the referee's count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up quickly, noticeable damage appearing under his eye as the fighters exchanged hard punches.
The challenger, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor narrowly won the verdict with scoring tallies of draw, close margin and 115-112, but each competitor were relentless and brave, all the qualities their inspiration Hatton stood for.
