British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the approaches failed to mesh, with excessive holding disrupting the fight.
Two judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Various analysts thought Parker, thirty-one, merited the victory but the Derbyshire fighter endured the second loss of his 28-bout career.
Buatsi Secures Win in Slow Affair
The fighter's advancement has plateaued in recent years through management issues and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with both competitors prepared to take risks in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, causing problems for the favorite, who worked behind a protective stance to edge the more effective periods.
The spectators' acceptance diminished because of frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but many rounds were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to capture the European light heavyweight championship.
The arena grew hushed for a deeply poignant memorial ahead of the contest as ten bells tolled in remembrance of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the concluding sound faded, the silence became a chant of "there's only one Ricky Hatton".
The fighting within the ring reflected the sentiment. The eventual winner was knocked down by a powerful punch squarely on the chin in the early round, rising shakily to his footing on the count of eight.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, noticeable damage appearing under his eye as the duo traded punishing blows.
Rea, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with official scores of even score, narrow lead and clearer margin, but the two athletes were determined and full of heart, exactly what their hero Hatton represented.
