British light heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a close ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a match where the styles didn't complement each other, with frequent clinching marring the contest.
The scoring judges had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest performance but what do champions do? They succeed," the victor commented in the arena as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
Buatsi Claims Victory in Dull Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand in the contest, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a tight guard to barely take the more effective rounds.
The spectators' acceptance diminished because of frequent holding, with the challenger slipping to the canvas various instances during grappling.
The underdog ended stronger, but many rounds were hard to judge. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a excellent local rivalry fight to capture the European light heavyweight championship.
The arena grew hushed for a extremely emotional homage before the fight as a bell ceremony sounded in memory of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell disappeared, the silence gave way to a roar of "there's just one Hatton".
The fighting within the ring equaled the sentiment. Arthur was floored by a left hook flush on the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged early, heavy swelling forming under his face as the duo landed hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor barely secured the verdict with official scores of 114-114, 115-113 and 115-112, but each competitor were persistent and full of heart, everything their hero Hatton stood for.
