UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a tight ten-round fight at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a fight where the approaches failed to mesh, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but what defines champions? They succeed," Buatsi stated in the ringside as he was faced boos from the spectators.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-bout career.
Buatsi Claims Victory in Dull Affair
Buatsi's progress has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He started carefully, with both competitors ready to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance wore thin amid frequent holding, with Parker falling to the floor several times during clinches.
The underdog ended stronger, but several stanzas were hard to judge. However, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur overcame Rea by split-decision in a outstanding Manchester vs Manchester contest to win the European light-heavyweight championship.
The arena became quiet for a profoundly moving tribute ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell faded, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting within the ring reflected the emotion. Arthur was knocked down by a left hook flush on the face in the second round, rising shakily to his feet on the count of eight.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, the opponent - in competitive blue - was injured quickly, noticeable damage developing under his face as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of draw, 115-113 and clearer margin, but each competitor were determined and courageous, everything their hero the legend embodied.
