British light-heavyweight Buatsi earned a win yet underwhelming start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight ten-round contest at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a fight where the techniques never quite clicked, with frequent clinching marring the contest.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi said in the ringside as he was met by disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts felt Parker, 31, deserved the decision but the Derbyshire fighter endured the second defeat of his 28-match career.
Buatsi Claims Victory in Slow Affair
Buatsi's progress has stalled in the past few years through management issues and considerable time of lack of fights.
Earlier forecast as the future of British boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to narrowly win the better periods.
The crowd's patience diminished because of frequent holding, with Parker going down several times during close exchanges.
Parker closed well, but several stanzas were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a excellent local rivalry battle to capture the European light-heavyweight title.
The arena fell silent for a extremely emotional homage prior to the bout as ten bells rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the urban center since Hatton's death. As the last bell ended, the quiet became a chant of "there's only one Ricky Hatton".
The action inside the ropes equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the chin in the initial stage, standing uncertainly to his position on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his orbital area as the duo landed powerful shots.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the decision with judges scorecards of even score, 115-113 and clearer margin, but each competitor were relentless and full of heart, everything their idol Hatton represented.
