British light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round fight at the Manchester venue.
But Parker had his moments, connecting with powerful clean blows in a match where the approaches failed to mesh, with frequent clinching spoiling the contest.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," the victor commented in the ringside as he was met by boos from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the victory but the British boxer suffered the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Slow Affair
The fighter's advancement has plateaued in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a cagey opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who operated with a solid defense to edge the cleaner periods.
The spectators' acceptance diminished because of constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a outstanding local rivalry contest to capture the continental title.
The arena fell silent for a deeply poignant tribute prior to the bout as a bell ceremony sounded in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the last bell ended, the stillness gave way to a chant of "only one Hatton".
The competition within the ring reflected the feeling. The eventual winner was sent to the canvas by a left hook flush on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was injured early, significant bruising forming under his face as the duo landed hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity hardly diminished over the full distance.
The victor edged the decision with judges scorecards of even score, 115-113 and clearer margin, but each competitor were determined and full of heart, exactly what their inspiration the legend embodied.
