UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a match where the styles never quite clicked, with constant grabbing spoiling the action.
The officials had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They succeed," the victor stated in the ringside as he was met by boos from the audience.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts thought Parker, thirty-one, should have been awarded the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Earns Victory in Uneventful Encounter
The fighter's advancement has plateaued in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the next star of British boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors willing to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to narrowly win the better periods.
The crowd's patience decreased amid frequent holding, with the challenger going down several times during grappling.
Parker ended stronger, but multiple periods were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to win the continental belt.
The stadium grew hushed for a deeply poignant homage prior to the bout as ten bells tolled in honor of Manchester's own Hatton, who died aged 46 in recently.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound ended, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a left hook flush on the face in the early round, rising shakily to his position on the referee's count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was marked up soon, heavy swelling appearing under his eye as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor edged the decision with judges scorecards of even score, narrow lead and clearer margin, but the two athletes were relentless and brave, exactly what their idol Hatton embodied.
