British light heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive ten-round bout at the boxing arena.
But the challenger found success, delivering effective individual punches in a contest where the styles didn't complement each other, with excessive holding disrupting the fight.
The officials judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They prevail," Buatsi said in the arena as he was met by negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the victory but the British boxer experienced the second defeat of his 28-match professional journey.
Buatsi Secures Triumph in Dull Match
Buatsi's progress has slowed in recent times through management issues and long spells of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with the two boxers ready to overcommit in a tentative opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who utilized a protective stance to narrowly win the more effective stanzas.
The audience's tolerance wore thin because of frequent holding, with Parker going down several times during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight title.
The venue became quiet for a extremely emotional tribute prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell disappeared, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition within the ring reflected the feeling. Arthur was floored by a significant blow squarely on the chin in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was damaged early, significant bruising appearing under his orbital area as the pair landed powerful shots.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor edged the decision with judges scorecards of draw, close margin and 115-112, but the two athletes were persistent and full of heart, everything their hero the legend embodied.
