British light heavyweight Buatsi earned a win yet disappointing debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the boxing arena.
But the challenger found success, landing some telling single shots in a match where the techniques failed to mesh, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They win," Buatsi said in the ringside as he was greeted with disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers believed Parker, 31, merited the victory but the contender suffered the second setback of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Affair
His career development has stalled in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to narrowly win the better stanzas.
The crowd's patience decreased amid regular grabbing, with Parker going down various instances during clinches.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Inspires Manchester Derby Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester battle to win the European light heavyweight title.
The stadium grew hushed for a extremely emotional tribute prior to the bout as ten bells rang in memory of the city's native Hatton, who died aged 46 in last month.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell faded, the quiet became a shout of "only one Ricky Hatton".
The action inside the ropes reflected the emotion. The eventual winner was knocked down by a significant blow flush on the jaw in the initial stage, rising shakily to his feet on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured early, noticeable damage forming under his orbital area as the pair traded powerful shots.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the decision with judges scorecards of 114-114, 115-113 and clearer margin, but both fighters were persistent and full of heart, exactly what their inspiration Hatton represented.
