UK light heavyweight Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a match where the techniques failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest performance but what defines champions? They prevail," the victor said in the arena as he was faced negative reactions from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, should have been awarded the victory but the contender endured the second loss of his 28-match professional journey.
Buatsi Secures Win in Uneventful Match
Buatsi's progress has stalled in recent years through promotional disputes and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to take risks in a tentative opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for the favorite, who operated with a protective stance to barely take the more effective rounds.
The spectators' acceptance diminished because of regular grabbing, with Parker going down multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur overcame Rea by split-decision in a terrific local rivalry contest to win the European light heavyweight title.
The stadium fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The action within the ring matched the emotion. Arthur was floored by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the count of eight.
But the traditional red attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was marked up soon, noticeable damage developing under his orbital area as the duo landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor barely secured the result with official scores of draw, close margin and 115-112, but the two athletes were persistent and brave, exactly what their inspiration Hatton represented.
