UK light heavyweight Buatsi earned a win yet underwhelming debut to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a fight where the approaches didn't complement each other, with excessive holding disrupting the fight.
The officials had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor stated in the ringside as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Several boxing experts thought the challenger, 31, should have been awarded the decision but the contender endured the second setback of his 28-match career.
Buatsi Secures Triumph in Uneventful Affair
His career development has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter willing to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who worked behind a tight guard to narrowly win the more effective periods.
The audience's tolerance decreased amid regular grabbing, with the challenger going down various instances during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. However, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur beat Rea by divided decision in a terrific local rivalry contest to capture the European light-heavyweight title.
The arena became quiet for a extremely emotional tribute prior to the bout as ten bells rang in remembrance of the city's native Hatton, who succumbed at age 46 in September.
It was the first major televised fight night in the urban center since the passing of Hatton. As the final chime faded, the silence became a shout of "there's only one Ricky Hatton".
The competition inside the ropes matched the sentiment. Arthur was floored by a significant blow flush on the face in the second round, rising shakily to his position on the referee's count.
But the red-colored equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling developing under his orbital area as the pair landed powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
Arthur barely secured the verdict with official scores of draw, close margin and 115-112, but both fighters were persistent and full of heart, exactly what their idol Hatton stood for.
