UK light-heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a match where the techniques never quite clicked, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best display but what do champions do? They win," Buatsi commented in the ring as he was faced negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, merited the decision but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Earns Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through contract problems and considerable time of lack of fights.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better periods.
The audience's tolerance decreased because of constant clinching, with the challenger falling to the floor various instances during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry fight to win the European light-heavyweight championship.
The arena fell silent for a extremely emotional tribute before the fight as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the final chime disappeared, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting within the ring matched the feeling. Arthur was sent to the canvas by a significant blow directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured soon, significant bruising forming under his orbital area as the fighters exchanged punishing blows.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the decision with official scores of 114-114, 115-113 and wider gap, but both fighters were relentless and full of heart, everything their idol the legend represented.
