UK light heavyweight Buatsi earned a win yet underwhelming beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the action.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi stated in the ringside as he was greeted with disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought Parker, 31, should have been awarded the decision but the contender endured the second setback of his 28-fight career.
Buatsi Earns Victory in Dull Affair
The fighter's advancement has plateaued in recent times through management issues and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to take risks in a cagey early stages.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was making just his second fight at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to barely take the cleaner stanzas.
The spectators' acceptance decreased amid frequent holding, with Parker slipping to the canvas various instances during clinches.
The underdog finished the stronger, but multiple periods were hard to judge. Although, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific local rivalry battle to capture the European light-heavyweight belt.
The venue grew hushed for a profoundly moving tribute ahead of the contest as ten bells sounded in honor of Manchester's own Hatton, who died 46 years old in last month.
It was the first major televised match card in the city since Hatton's passing. As the concluding sound faded, the stillness gave way to a chant of "there's just one Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was knocked down by a left hook flush on the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. On the opposite side, the opponent - in rival City blue - was injured soon, noticeable damage forming under his face as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur narrowly won the decision with official scores of draw, close margin and 115-112, but both fighters were relentless and courageous, exactly what their inspiration Hatton embodied.
