UK light heavyweight Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the approaches never quite clicked, with frequent clinching marring the contest.
The scoring judges scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi commented in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
Buatsi Claims Win in Slow Match
Buatsi's progress has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who utilized a solid defense to edge the cleaner rounds.
The crowd's patience diminished because of frequent holding, with Parker going down various instances during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Fight
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to secure the European light heavyweight championship.
The venue fell silent for a extremely emotional memorial ahead of the contest as ten bells sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the final chime ended, the quiet transitioned to a roar of "there's just one Hatton".
The action inside the ropes reflected the emotion. The eventual winner was knocked down by a left hook directly to the face in the initial stage, standing uncertainly to his position on the eight count.
But the red-colored equipment of the fighter soon came forward again. Across the ring, the opponent - in rival City blue - was marked up quickly, noticeable damage developing under his eye as the duo traded punishing blows.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the decision with judges scorecards of 114-114, 115-113 and wider gap, but both fighters were persistent and full of heart, all the qualities their idol the legend stood for.
