UK light-heavyweight Buatsi earned a win yet underwhelming start 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 split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a match where the approaches didn't complement each other, with excessive holding spoiling the fight.
Two judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what defines champions? They prevail," the victor stated in the ringside as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Various analysts felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter suffered the second setback of his 28-fight career.
Buatsi Claims Victory in Slow Encounter
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second appearance at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The spectators' acceptance decreased amid constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the European light-heavyweight belt.
The stadium fell silent for a profoundly moving memorial ahead of the contest as ten bells tolled in memory of local hero Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The action inside the ropes equaled the feeling. The eventual winner was knocked down by a significant blow squarely on the jaw in the second round, getting up unsteadily to his feet on the eight count.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was injured early, heavy swelling appearing under his face as the pair exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the action seldom decreased over 12 rounds.
The victor narrowly won the decision with official scores of 114-114, narrow lead and clearer margin, but each competitor were determined and brave, exactly what their inspiration the legend embodied.
