British light heavyweight Buatsi earned a win yet unimpressive beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round bout at the boxing arena.
But the challenger found success, connecting with powerful clean blows in a fight where the styles failed to mesh, with constant grabbing spoiling the contest.
Two judges had it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest showing but what defines champions? They win," Buatsi said in the arena as he was faced boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts felt Parker, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-fight career.
Buatsi Claims Triumph in Uneventful Match
The fighter's advancement has plateaued in recent times through management issues and extended periods of lack of fights.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under recent support.
He began cautiously, with neither fighter ready to overcommit in a tentative opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a solid defense to edge the cleaner rounds.
The crowd's patience wore thin because of frequent holding, with the challenger slipping to the canvas various instances during clinches.
Parker closed well, but multiple periods were hard to judge. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to secure the European light-heavyweight title.
The stadium fell silent for a extremely emotional tribute prior to the bout as ten bells sounded in memory of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the premier televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the quiet became a chant of "only one Ricky Hatton".
The fighting during the bout matched the emotion. The eventual winner was sent to the canvas by a left hook flush on the jaw in the early round, standing uncertainly to his footing on the eight count.
But the red-colored shorts of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was injured quickly, noticeable damage appearing under his orbital area as the fighters traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over 12 rounds.
Arthur barely secured the result with scoring tallies of draw, close margin and 115-112, but both fighters were determined and courageous, everything their idol the legend embodied.
