UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But Parker found success, connecting with powerful single shots in a match where the techniques failed to mesh, with frequent clinching marring the contest.
The officials had it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi stated in the ringside as he was faced boos from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers believed the challenger, 31, merited the win but the contender suffered the second loss of his 28-match professional journey.
Buatsi Secures Victory in Slow Encounter
Buatsi's progress has plateaued in the past few years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to overcommit in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance wore thin during regular grabbing, with Parker slipping to the canvas various instances during clinches.
The underdog closed well, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter Benavidez, and Russian champion Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to capture the continental belt.
The stadium fell silent for a deeply poignant tribute ahead of the contest as ten bells tolled in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime disappeared, the stillness transitioned to a chant of "there's only one Hatton".
The action within the ring reflected the emotion. Arthur was knocked down by a powerful punch flush on the face in the initial stage, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was damaged soon, noticeable damage forming under his eye as the pair traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor barely secured the verdict with judges scorecards of even score, narrow lead and wider gap, but the two athletes were persistent and full of heart, all the qualities their idol Hatton represented.
