UK light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective single shots in a fight where the techniques failed to mesh, with excessive holding disrupting the fight.
The officials had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They succeed," Buatsi said in the ring as he was met by boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought Parker, 31, should have been awarded the victory but the contender endured the second loss of his 28-bout career.
The Champion Secures Win in Dull Encounter
Buatsi's progress has plateaued in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who worked behind a protective stance to edge the more effective stanzas.
The audience's tolerance decreased amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
Parker closed well, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter David 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 Battle
In the co-main event, Arthur defeated Rea by divided decision in a outstanding all-Manchester contest to capture the continental championship.
The arena became quiet for a profoundly moving memorial ahead of the contest as 10 bells tolled in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the stillness gave way to a shout of "only one Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the jaw in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage developing under his eye as the pair landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur narrowly won the verdict with scoring tallies of draw, 115-113 and wider gap, but the two athletes were relentless and courageous, exactly what their hero the legend embodied.
