UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, delivering effective individual punches in a fight where the styles never quite clicked, with constant grabbing marring the fight.
Two judges scored it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi commented in the ring as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the victory but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Earns Victory in Uneventful Affair
The fighter's advancement has stalled in recent years through promotional disputes and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective periods.
The audience's tolerance decreased amid regular grabbing, with Parker going down various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry contest to win the continental title.
The arena became quiet for a profoundly moving memorial ahead of the contest as 10 bells rang in remembrance of local hero Ricky Hatton, who died aged 46 in recently.
It was the premier televised match card in the location since the passing of Hatton. As the last bell ended, the silence gave way to a roar of "only one Hatton".
The competition during the bout matched the sentiment. The eventual winner was knocked down by a significant blow flush on the jaw in the second round, rising shakily to his feet on the eight count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was injured quickly, heavy swelling developing under his orbital area as the pair traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the verdict with judges scorecards of even score, close margin and clearer margin, but each competitor were persistent and courageous, exactly what their hero the legend embodied.
