British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the approaches never quite clicked, with constant grabbing spoiling the fight.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best display but what do champions do? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts felt the challenger, 31, merited the victory but the British boxer suffered the second setback of his 28-bout career.
Buatsi Secures Triumph in Uneventful Encounter
His career development has plateaued in the past few years through contract problems and extended periods of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He started carefully, with neither fighter prepared to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to narrowly win the cleaner rounds.
The audience's tolerance decreased during regular grabbing, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light-heavyweight title.
The arena became quiet for a deeply poignant tribute prior to the bout as ten bells rang in honor of the city's native Hatton, who succumbed aged 46 in September.
It was the first major televised match card in the city since Hatton's passing. As the final chime disappeared, the quiet gave way to a roar of "only one Ricky Hatton".
The competition within the ring matched the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the early round, rising shakily to his feet on the eight count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, the opponent - in opposing blue - was injured quickly, noticeable damage developing under his face as the pair traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur narrowly won the decision with official scores of draw, narrow lead and 115-112, but both fighters were persistent and full of heart, all the qualities their inspiration the legend stood for.
