UK light heavyweight Buatsi earned a win yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close ten-round fight at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with frequent clinching spoiling the fight.
The scoring judges had it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest display but what do champions do? They succeed," Buatsi commented in the ringside as he was met by boos from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Various analysts believed Parker, 31, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-match professional journey.
The Champion Secures Win in Uneventful Match
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what feels like a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who operated with a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished amid frequent holding, with the challenger slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to win the European light heavyweight title.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells sounded in remembrance of the city's native Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the final chime disappeared, the stillness became a roar of "there's just one Hatton".
The fighting inside the ropes equaled the emotion. Arthur was sent to the canvas by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the traditional red attire of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged soon, heavy swelling forming under his face as the pair exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor barely secured the verdict with judges scorecards of even score, close margin and wider gap, but each competitor were relentless and full of heart, everything their idol Hatton represented.
