UK light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round bout at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the approaches failed to mesh, with constant grabbing marring the contest.
The scoring judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my greatest display but what defines champions? They win," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt the challenger, 31, merited the win but the British boxer endured the second loss of his 28-bout career.
Buatsi Secures Triumph in Slow Encounter
His career development has slowed in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors prepared to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance diminished because of constant clinching, with Parker slipping to the canvas several times during grappling.
Parker closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a terrific local rivalry fight to capture the European light-heavyweight championship.
The stadium fell silent for a profoundly moving homage ahead of the contest as ten bells rang in memory of local hero Hatton, who died 46 years old in September.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the silence became a roar of "there's only one Hatton".
The fighting inside the ropes reflected the sentiment. The eventual winner was knocked down by a powerful punch squarely on the chin in the initial stage, rising shakily to his position on the referee's count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was injured early, heavy swelling developing under his eye as the duo traded punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the intensity seldom decreased over twelve rounds.
The victor edged the verdict with scoring tallies of even score, close margin and clearer margin, but both fighters were persistent and brave, all the qualities their hero the legend embodied.
