UK light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with constant grabbing spoiling the contest.
Two judges judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," the victor stated in the ringside as he was greeted with boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Several boxing experts thought Parker, thirty-one, deserved the victory but the contender experienced the second setback of his 28-fight career.
Buatsi Earns Triumph in Dull Affair
His career development has slowed in recent years through management issues and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He started carefully, with neither fighter ready to take risks in a tentative opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to edge the more effective rounds.
The crowd's patience wore thin amid frequent holding, with the challenger slipping to the canvas multiple occasions during grappling.
Parker closed well, but multiple periods were difficult to score. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Battle
In the co-main event, Arthur overcame Rea by split-decision in a terrific Manchester vs Manchester contest to capture the European light-heavyweight title.
The arena grew hushed for a extremely emotional memorial before the fight as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the premier televised boxing event in the urban center since Hatton's passing. As the last bell faded, the quiet gave way to a shout of "only one Hatton".
The competition inside the ropes reflected the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the early round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was injured soon, noticeable damage forming under his orbital area as the pair exchanged punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the decision with official scores of 114-114, close margin and 115-112, but each competitor were persistent and full of heart, everything their idol Hatton stood for.
