British light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a competitive 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a fight where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges had it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi commented in the ring as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts felt the challenger, thirty-one, deserved the win but the British boxer experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Slow Encounter
His career development has plateaued in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who operated with a tight guard to edge the cleaner rounds.
The audience's tolerance decreased amid regular grabbing, with Parker slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
The victor progresses, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry fight to secure the European light heavyweight championship.
The venue became quiet for a profoundly moving homage prior to the bout as 10 bells tolled in honor of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the concluding sound disappeared, the silence transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring equaled the emotion. The eventual winner was knocked down by a powerful punch squarely on the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the Manchester United-red attire of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was damaged quickly, significant bruising appearing under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action seldom decreased over the full distance.
The victor narrowly won the result with official scores of draw, 115-113 and clearer margin, but the two athletes were persistent and full of heart, all the qualities their hero the legend represented.
