British light heavyweight Buatsi made a winning yet disappointing start to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the action.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but what defines champions? They prevail," Buatsi commented in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the victory but the Derbyshire fighter experienced the second loss of his 28-bout career.
Buatsi Earns Win in Slow Affair
His career development has plateaued in recent times through contract problems and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with both competitors ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the better periods.
The audience's tolerance decreased during constant clinching, with Parker slipping to the canvas several times during clinches.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the likes of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Motivates Local Rivalry Contest
In the secondary fight, Arthur defeated Rea by close verdict in a terrific all-Manchester contest to secure the European light heavyweight title.
The arena became quiet for a extremely emotional tribute prior to the bout as ten bells sounded in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the concluding sound faded, the stillness became a shout of "there's only one Hatton".
The fighting during the bout equaled the feeling. The eventual winner was floored by a left hook squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up quickly, heavy swelling appearing under his orbital area as the pair landed punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the verdict with official scores of 114-114, close margin and wider gap, but each competitor were determined and courageous, everything their idol the legend stood for.
