British light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a match where the approaches never quite clicked, with excessive holding disrupting the action.
The officials judged it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They succeed," the victor commented in the arena as he was met by disapproval from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Various analysts thought the challenger, 31, merited the victory but the contender endured the second setback of his 28-bout career.
Buatsi Claims Victory in Uneventful Affair
The fighter's advancement has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to overcommit in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to narrowly win the better stanzas.
The audience's tolerance diminished because of frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Contest
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific all-Manchester battle to capture the European light heavyweight belt.
The arena fell silent for a extremely emotional homage ahead of the contest as 10 bells tolled in remembrance of Manchester's own Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime faded, the silence gave way to a chant of "only one Hatton".
The fighting during the bout equaled the feeling. The eventual winner was floored by a left hook directly to the jaw in the early round, rising shakily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was damaged quickly, heavy swelling developing under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
The victor edged the decision with official scores of 114-114, close margin and wider gap, but each competitor were determined and full of heart, all the qualities their hero Hatton stood for.
