UK light heavyweight Buatsi secured a victory yet disappointing debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But the challenger found success, delivering effective individual punches in a contest where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The officials had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," the victor commented in the ring as he was faced disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts thought the challenger, thirty-one, deserved the win but the Derbyshire fighter suffered the second defeat of his 28-match professional journey.
The Champion Secures Win in Dull Match
Buatsi's progress has slowed in recent times through management issues and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with neither fighter prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the better rounds.
The audience's tolerance diminished because of regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Motivates All-Manchester Battle
In the co-main event, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester battle to win the continental belt.
The arena became quiet for a extremely emotional memorial prior to the bout as ten bells rang in remembrance of Manchester's own Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the last bell disappeared, the quiet transitioned to a shout of "there's only one Hatton".
The competition inside the ropes matched the sentiment. Arthur was sent to the canvas by a powerful punch squarely on the chin in the early round, rising shakily to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was marked up early, noticeable damage developing under his face as the pair landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur edged the result with judges scorecards of 114-114, narrow lead and 115-112, but the two athletes were persistent and courageous, exactly what their hero Hatton represented.
