British light heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight ten-round contest at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the styles never quite clicked, with constant grabbing spoiling the fight.
The officials scored it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ring as he was met by disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Earns Triumph in Dull Match
Buatsi's progress has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to realize his potential - perhaps in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter willing to take risks in a cagey early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who utilized a solid defense to narrowly win the cleaner stanzas.
The crowd's patience diminished because of regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Hatton Tribute Inspires Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester fight to win the European light-heavyweight title.
The arena grew hushed for a profoundly moving memorial before the fight as a bell ceremony tolled in honor of local hero Ricky Hatton, who passed away aged 46 in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell ended, the stillness transitioned to a roar of "there's just one Hatton".
The fighting within the ring equaled the emotion. Arthur was sent to the canvas by a powerful punch flush on the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was damaged quickly, significant bruising forming under his face as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur edged the result with judges scorecards of 114-114, narrow lead and clearer margin, but each competitor were persistent and brave, exactly what their idol Hatton stood for.
