UK light heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a match where the styles never quite clicked, with constant grabbing spoiling the contest.
The officials had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best display but what defines champions? They win," Buatsi stated in the ringside as he was faced negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Various analysts believed the challenger, 31, merited the win but the Derbyshire fighter experienced the second loss of his 28-fight career.
The Champion Earns Triumph in Slow Match
His career development has plateaued in recent times through contract problems and extended periods of lack of fights.
Previously predicted as the next star of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for the favorite, who operated with a tight guard to barely take the more effective stanzas.
The audience's tolerance diminished amid frequent holding, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Fuels All-Manchester Contest
In the supporting bout, Arthur overcame Rea by close verdict in a terrific local rivalry fight to secure the European light heavyweight championship.
The arena became quiet for a profoundly moving memorial before the fight as ten bells tolled in remembrance of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the silence transitioned to a roar of "there's only one Ricky Hatton".
The competition within the ring equaled the emotion. Arthur was knocked down by a significant blow flush on the face in the second round, standing uncertainly to his position on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was marked up soon, noticeable damage appearing under his face as the duo landed hard punches.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
The victor edged the verdict with scoring tallies of draw, narrow lead and clearer margin, but each competitor were determined and courageous, exactly what their hero the legend stood for.
