UK light heavyweight Buatsi earned a win yet unimpressive beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger had his moments, landing some telling single shots in a fight where the techniques never quite clicked, with constant grabbing disrupting the contest.
Two judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi said in the ring as he was met by boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed the challenger, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-fight professional journey.
Buatsi Secures Win in Dull Affair
His career development has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter ready to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The spectators' acceptance wore thin because of regular grabbing, with Parker going down multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Memorial Motivates Local Rivalry Battle
In the secondary fight, Arthur defeated Rea by close verdict in a terrific all-Manchester contest to secure the European light-heavyweight championship.
The arena grew hushed for a extremely emotional homage ahead of the contest as ten bells rang in honor of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the location since Hatton's passing. As the concluding sound ended, the quiet became a chant of "there's just one Hatton".
The competition during the bout equaled the feeling. Arthur was knocked down by a left hook flush on the jaw in the initial stage, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in competitive blue - was damaged soon, significant bruising developing under his face as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the pace rarely dropped over the full distance.
Arthur narrowly won the decision with judges scorecards of draw, close margin and clearer margin, but each competitor were relentless and brave, exactly what their hero the legend stood for.
