UK light heavyweight Buatsi earned a win yet underwhelming beginning to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing marring the action.
Two judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my finest showing but what defines champions? They win," the victor commented in the ring as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to earn a 20th pro success.
Some ringside observers thought Parker, thirty-one, merited the victory but the Derbyshire fighter endured the second loss of his 28-match career.
Buatsi Secures Victory in Dull Encounter
His career development has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a tight guard to edge the cleaner stanzas.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Fuels Manchester Derby Contest
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester fight to capture the European light heavyweight championship.
The stadium grew hushed for a profoundly moving memorial ahead of the contest as 10 bells tolled in memory of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound disappeared, the stillness gave way to a shout of "there's just one Ricky Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a powerful punch flush on the jaw in the second round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. On the opposite side, the opponent - in opposing blue - was injured soon, significant bruising forming under his orbital area as the fighters exchanged punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur barely secured the decision with official scores of even score, close margin and clearer margin, but each competitor were determined and full of heart, everything their idol Hatton represented.
