UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective clean blows in a contest where the approaches never quite clicked, with excessive holding marring the action.
The officials scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my finest performance but what do champions do? They succeed," the victor stated in the arena as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts felt Parker, 31, should have been awarded the decision but the British boxer experienced the second loss of his 28-bout career.
The Champion Earns Triumph in Uneventful Encounter
Buatsi's progress has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to realize his potential - maybe in what seems like a last chance - under recent support.
He began cautiously, with the two boxers prepared to take risks in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective rounds.
The audience's tolerance diminished during frequent holding, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but many rounds were difficult to score. However, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester fight to capture the European light-heavyweight title.
The arena became quiet for a deeply poignant homage before the fight as 10 bells tolled in memory of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised match card in the city since Hatton's passing. As the final chime ended, the silence transitioned to a roar of "there's only one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored equipment of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was damaged quickly, noticeable damage appearing under his eye as the fighters traded hard punches.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the result with scoring tallies of draw, 115-113 and 115-112, but each competitor were relentless and courageous, all the qualities their idol Hatton stood for.
