British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close ten-round contest at the Manchester venue.
But Parker had his moments, landing some telling single shots in a contest where the styles never quite clicked, with constant grabbing spoiling the contest.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," Buatsi said in the arena as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, merited the win but the contender suffered the second loss of his 28-match professional journey.
Buatsi Claims Triumph in Slow Match
The fighter's advancement has slowed in recent times through management issues and extended periods of inactivity.
Previously predicted as the next star of the British fight scene, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to overcommit in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the better periods.
The audience's tolerance wore thin because of regular grabbing, with Parker falling to the floor several times during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Hatton Memorial Motivates Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by split-decision in a terrific local rivalry battle to win the European light heavyweight title.
The arena fell silent for a deeply poignant tribute before the fight as 10 bells sounded in honor of Manchester's own Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the city since the passing of Hatton. As the last bell faded, the silence transitioned to a roar of "there's only one Hatton".
The competition within the ring reflected the sentiment. The eventual winner was knocked down by a powerful punch squarely on the face in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up early, noticeable damage appearing under his eye as the fighters traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor edged the result with judges scorecards of even score, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their idol the legend represented.
