British light heavyweight Buatsi made a winning yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a match where the techniques didn't complement each other, with frequent clinching marring the fight.
The officials scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi commented in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Several boxing experts thought the challenger, 31, should have been awarded the win but the British boxer experienced the second setback of his 28-match professional journey.
The Champion Secures Win in Uneventful Affair
Buatsi's progress has plateaued in recent years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a solid defense to barely take the better rounds.
The crowd's patience decreased because of regular grabbing, with the challenger slipping to the canvas several times during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Although, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the caliber of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light heavyweight championship.
The stadium grew hushed for a extremely emotional homage ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound faded, the quiet gave way to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was sent to the canvas by a powerful punch flush on the face in the second round, getting up unsteadily to his feet on the referee's count.
But the traditional red attire of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured soon, significant bruising appearing under his face as the pair exchanged hard punches.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the pace hardly diminished over the full distance.
Arthur narrowly won the result with official scores of 114-114, close margin and wider gap, but the two athletes were persistent and brave, everything their idol Hatton represented.
