UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight ten-round fight at the boxing arena.
But Parker had his moments, delivering effective individual punches in a match where the techniques didn't complement each other, with excessive holding disrupting the action.
The scoring judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what defines champions? They prevail," the victor commented in the ring as he was faced negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the victory but the contender suffered the second defeat of his 28-fight career.
Buatsi Secures Win in Dull Match
The fighter's advancement has plateaued in recent times through promotional disputes and considerable time of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a last chance - under fresh management.
He started carefully, with both competitors prepared to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who operated with a tight guard to edge the cleaner rounds.
The crowd's patience decreased during frequent holding, with the challenger falling to the floor multiple occasions during clinches.
The underdog closed well, but multiple periods were hard to judge. Although, previous titleholder Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to win the European light-heavyweight belt.
The arena grew hushed for a deeply poignant memorial ahead of the contest as a bell ceremony rang in memory of the city's native Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell ended, the silence became a chant of "only one Ricky Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was sent to the canvas by a left hook directly to the chin in the early round, standing uncertainly to his feet on the eight count.
But the red-colored equipment of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was damaged quickly, heavy swelling forming under his face as the pair traded hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur narrowly won the decision with scoring tallies of draw, close margin and clearer margin, but both fighters were relentless and courageous, exactly what their inspiration Hatton stood for.
