UK light heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close 10-round fight at the Manchester venue.
But the challenger found success, landing some telling individual punches in a match where the styles never quite clicked, with frequent clinching disrupting the contest.
The scoring judges scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They win," the victor said in the arena as he was met by negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the decision but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors willing to overcommit in a tentative initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The audience's tolerance decreased because of constant clinching, with Parker going down various instances during grappling.
Parker closed well, but several stanzas were difficult to score. However, ex-champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester fight to win the European light-heavyweight title.
The arena became quiet for a extremely emotional memorial ahead of the contest as a bell ceremony rang in honor of local hero Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the final chime ended, the quiet became a chant of "there's only one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a significant blow flush on the chin in the second round, rising shakily to his position on the eight count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was injured early, heavy swelling forming under his eye as the duo exchanged powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the verdict with scoring tallies of 114-114, close margin and wider gap, but the two athletes were determined and brave, all the qualities their hero Hatton represented.
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