UK light-heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a match where the techniques never quite clicked, with excessive holding spoiling the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best display but what defines champions? They succeed," the victor commented in the arena as he was faced negative reactions from the spectators.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts felt Parker, 31, deserved the victory but the contender suffered the second loss of his 28-bout career.
The Champion Claims Win in Slow Match
The fighter's advancement 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 achieve expectations - perhaps in what feels like a last chance - under fresh management.
He began cautiously, with neither fighter ready to overcommit in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who worked behind a tight guard to narrowly win the more effective rounds.
The spectators' acceptance decreased because of frequent holding, with Parker slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Motivates Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the concluding sound disappeared, the silence became a chant of "only one Ricky Hatton".
The competition during the bout matched the emotion. Arthur was sent to the canvas by a left hook squarely on the jaw in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured soon, heavy swelling developing under his face as the pair exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur barely secured the decision with official scores of 114-114, close margin and wider gap, but both fighters were determined and brave, everything their hero the legend embodied.
