UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a match where the techniques didn't complement each other, with frequent clinching marring the contest.
The officials judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was met by negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers felt Parker, 31, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Secures Triumph in Dull Match
Buatsi's progress has plateaued in recent times through contract problems and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to overcommit in a tentative opening few rounds.
Parker, whose only previous defeat 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 kept it close, creating difficulties for Buatsi, who worked behind a protective stance to narrowly win the more effective periods.
The spectators' acceptance diminished because of frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Hatton Memorial Inspires Manchester Derby Contest
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to secure the continental championship.
The venue became quiet for a deeply poignant tribute before the fight as ten bells rang in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound disappeared, the stillness gave way to a chant of "there's only one Ricky Hatton".
The competition during the bout equaled the feeling. The eventual winner was knocked down by a significant blow flush on the chin in the early round, standing uncertainly to his feet 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 marked up early, significant bruising developing under his eye as the pair landed hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the result with official scores of 114-114, 115-113 and 115-112, but the two athletes were persistent and courageous, all the qualities their hero the legend represented.
