UK light-heavyweight Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close ten-round contest at the boxing arena.
But Parker found success, connecting with powerful clean blows in a fight where the techniques never quite clicked, with frequent clinching spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what defines champions? They succeed," the victor stated in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the victory but the British boxer experienced the second defeat of his 28-bout professional journey.
Buatsi Claims Triumph in Dull Affair
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance wore thin amid constant clinching, with the challenger falling to the floor various instances during close exchanges.
Parker closed well, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Contest
In the co-main event, Arthur defeated Bradley Rea by split-decision in a excellent Manchester vs Manchester battle to win the European light-heavyweight belt.
The stadium became quiet for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the city since Hatton's death. As the final chime disappeared, the quiet gave way to a roar of "there's only one Ricky Hatton".
The competition inside the ropes matched the sentiment. Arthur was sent to the canvas by a powerful punch flush on the jaw in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up early, significant bruising appearing under his orbital area as the fighters landed hard punches.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur edged the decision with scoring tallies of 114-114, close margin and clearer margin, but each competitor were relentless and brave, exactly what their inspiration Hatton represented.
