UK light heavyweight Buatsi secured a victory yet unimpressive debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a contest where the approaches never quite clicked, with frequent clinching marring the contest.
The officials scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They prevail," the victor said in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers thought the challenger, 31, should have been awarded the decision but the contender experienced the second defeat of his 28-match career.
The Champion Secures Victory in Slow Encounter
The fighter's advancement has stalled in recent years through management issues and extended periods of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second appearance at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective rounds.
The spectators' acceptance diminished amid constant clinching, with Parker falling to the floor multiple occasions during grappling.
The underdog closed well, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to win the European light-heavyweight belt.
The venue fell silent for a extremely emotional memorial before the fight as ten bells rang in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the silence became a roar of "only one Hatton".
The competition inside the ropes matched the feeling. Arthur was sent to the canvas by a powerful punch squarely on the chin in the early round, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was injured soon, significant bruising forming under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the decision with official scores of even score, 115-113 and wider gap, but each competitor were determined and brave, all the qualities their hero the legend embodied.
