UK light-heavyweight Buatsi made a winning yet underwhelming debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful single shots in a match where the approaches never quite clicked, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my finest display but what do champions do? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Some ringside observers thought the challenger, 31, deserved the decision but the British boxer endured the second loss of his 28-match career.
Buatsi Earns Win in Slow Match
Buatsi's progress has plateaued in the past few years through contract problems and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who worked behind a solid defense to barely take the better stanzas.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas several times during clinches.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester fight to capture the continental title.
The stadium fell silent for a extremely emotional memorial before the fight as 10 bells sounded in remembrance of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime ended, the stillness transitioned to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the feeling. The eventual winner was floored by a powerful punch squarely on the face in the early round, rising shakily to his position on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured early, significant bruising forming under his face as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the decision with judges scorecards of draw, narrow lead and wider gap, but each competitor were determined and full of heart, everything their inspiration Hatton represented.
