British light-heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a match where the styles didn't complement each other, with constant grabbing marring the fight.
Two judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," the victor said in the ringside as he was greeted with disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts thought the challenger, 31, merited the victory but the Derbyshire fighter suffered the second loss of his 28-fight professional journey.
Buatsi Secures Victory in Dull Encounter
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future of British boxing, he now stands trying to fulfil that early promise - maybe in what feels like a last chance - under recent support.
He opened tentatively, with both competitors willing to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to barely take the better stanzas.
The crowd's patience decreased amid regular grabbing, with the challenger going down multiple occasions during clinches.
Parker ended stronger, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the continental title.
The arena became quiet for a profoundly moving tribute ahead of the contest as 10 bells rang in remembrance of the city's native Ricky Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the last bell disappeared, the stillness became a roar of "only one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was knocked down by a left hook squarely on the chin in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up quickly, significant bruising developing under his eye as the pair traded powerful shots.
The challenger, 27, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the decision with judges scorecards of even score, close margin and 115-112, but each competitor were determined and full of heart, exactly what their idol the legend represented.
