UK light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a match where the techniques didn't complement each other, with excessive holding disrupting the action.
Two judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my best display but what defines champions? They succeed," Buatsi stated in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought Parker, 31, merited the decision but the contender suffered the second loss of his 28-bout professional journey.
Buatsi Claims Win in Dull Affair
His career development has plateaued in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The crowd's patience decreased during frequent holding, with Parker going down various instances during grappling.
The underdog finished the stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Hatton Homage Inspires All-Manchester Contest
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight belt.
The arena became quiet for a profoundly moving homage prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the urban center since Hatton's passing. As the final chime faded, the quiet gave way to a shout of "there's only one Ricky Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up soon, noticeable damage developing under his eye as the pair landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the verdict with judges scorecards of 114-114, close margin and 115-112, but the two athletes were determined and brave, all the qualities their idol Hatton represented.
