UK light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But Parker had his moments, delivering effective individual punches in a fight where the styles never quite clicked, with frequent clinching disrupting the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but what do champions do? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th career victory.
Some ringside observers thought Parker, 31, deserved the win but the Derbyshire fighter endured the second setback of his 28-match career.
Buatsi Earns Victory in Uneventful Encounter
Buatsi's progress has stalled in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was making just his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who utilized a protective stance to narrowly win the cleaner stanzas.
The crowd's patience wore thin amid regular grabbing, with the challenger slipping to the canvas several times during grappling.
The underdog finished the stronger, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester contest to secure the continental title.
The arena became quiet for a extremely emotional homage prior to the bout as ten bells sounded in honor of Manchester's own Ricky Hatton, who passed away at age 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the final chime faded, the stillness became a roar of "there's only one Hatton".
The competition inside the ropes equaled the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the initial stage, rising shakily to his feet on the referee's count.
But the red-colored attire of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was injured quickly, significant bruising appearing under his eye as the duo traded hard punches.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the decision with official scores of even score, 115-113 and 115-112, but the two athletes were relentless and brave, everything their hero Hatton represented.
