UK light heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round fight at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the techniques failed to mesh, with constant grabbing marring the contest.
The officials scored it 96-94 for to the winner, with the final judge a 95-95 draw.
"It wasn't my best performance but what defines champions? They win," the victor stated in the ringside as he was faced negative reactions from the audience.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers believed Parker, 31, should have been awarded the win but the contender experienced the second setback of his 28-match career.
Buatsi Secures Win in Dull Match
Buatsi's progress has slowed in recent years through management issues and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to realize his potential - possibly in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers willing to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, making life awkward for the favorite, who utilized a protective stance to edge the better stanzas.
The audience's tolerance decreased during frequent holding, with the challenger slipping to the canvas various instances during clinches.
The underdog closed well, but multiple periods were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight championship.
The stadium became quiet for a extremely emotional tribute prior to the bout as ten bells rang in remembrance of Manchester's own Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the location since Hatton's death. As the final chime faded, the silence became a chant of "there's just one Hatton".
The fighting during the bout reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the traditional red attire of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was injured early, heavy swelling developing under his face as the pair traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the verdict with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were persistent and full of heart, exactly what their hero the legend stood for.
