British light-heavyweight Buatsi made a winning yet unimpressive debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a match where the techniques failed to mesh, with constant grabbing spoiling the fight.
Two judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They prevail," the victor said in the ringside as he was greeted with boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers felt the challenger, thirty-one, merited the win but the Derbyshire fighter experienced the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Dull Encounter
The fighter's advancement has stalled in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of British boxing, he now is positioned trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to overcommit in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who utilized a tight guard to edge the better periods.
The spectators' acceptance wore thin because of frequent holding, with Parker going down multiple occasions during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor progresses, but with the caliber of power puncher David Benavidez, and Russian star Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Arthur overcame Rea by close verdict in a outstanding all-Manchester contest to secure the continental belt.
The venue grew hushed for a profoundly moving homage before the fight as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the location since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a chant of "only one Hatton".
The action within the ring reflected the feeling. The eventual winner was knocked down by a significant blow squarely on the face in the initial stage, rising shakily to his footing on the eight count.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, heavy swelling developing under his face as the pair exchanged powerful shots.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the decision with judges scorecards of even score, 115-113 and 115-112, but each competitor were determined and brave, all the qualities their hero the legend represented.
