British light-heavyweight Buatsi earned a win yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a close ten-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a match where the approaches failed to mesh, with frequent clinching disrupting the contest.
Two judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest display but what do champions do? They win," Buatsi stated in the arena as he was met by negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the win but the British boxer experienced the second setback of his 28-fight career.
Buatsi Secures Triumph in Uneventful Encounter
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the future of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, causing problems for Buatsi, who operated with a solid defense to narrowly win the better periods.
The audience's tolerance decreased during regular grabbing, with Parker going down several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the presence of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Hatton Homage Fuels Local Rivalry Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to secure the European light-heavyweight title.
The arena grew hushed for a deeply poignant homage ahead of the contest as 10 bells tolled in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the premier televised match card in the urban center since Hatton's death. As the final chime faded, the quiet became a roar of "only one Hatton".
The action during the bout matched the emotion. Arthur was sent to the canvas by a powerful punch squarely on the chin in the early round, standing uncertainly to his position on the eight count.
But the red-colored shorts of the fighter soon came forward again. On the opposite side, the opponent - in rival City blue - was marked up quickly, noticeable damage forming under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor narrowly won the decision with scoring tallies of 114-114, 115-113 and clearer margin, but the two athletes were determined and full of heart, exactly what their hero the legend represented.
