UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a close ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing spoiling the fight.
The officials scored it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best performance but what defines champions? They succeed," the victor commented in the arena as he was greeted with boos from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in February - to secure a 20th career victory.
Various analysts believed the challenger, 31, merited the decision but the Derbyshire fighter endured the second defeat of his 28-match career.
Buatsi Claims Triumph in Uneventful Affair
His career development has plateaued in recent times through contract problems and considerable time of lack of fights.
Earlier forecast as the future of British boxing, he now is positioned trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to overcommit in a calculated initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better periods.
The crowd's patience wore thin amid frequent holding, with Parker going down various instances during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Memorial Fuels Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light heavyweight title.
The stadium fell silent for a extremely emotional memorial ahead of the contest as ten bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised fight night in the urban center since the passing of Hatton. As the last bell disappeared, the quiet transitioned to a chant of "only one Hatton".
The action within the ring reflected the sentiment. Arthur was sent to the canvas by a left hook flush on the jaw in the initial stage, rising shakily to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up early, heavy swelling forming under his face as the pair landed hard punches.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over the full distance.
The victor barely secured the result with official scores of even score, close margin and clearer margin, but both fighters were determined and full of heart, all the qualities their inspiration the legend represented.
