British light heavyweight Buatsi earned a win yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a fight where the styles didn't complement each other, with constant grabbing spoiling the action.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the arena as he was met by disapproval from the audience.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts thought Parker, 31, merited the victory but the contender endured the second defeat of his 28-match professional journey.
Buatsi Claims Win in Slow Match
The fighter's advancement has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a solid defense to barely take the cleaner rounds.
The spectators' acceptance diminished during frequent holding, with Parker going down various instances during clinches.
The underdog closed well, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a terrific local rivalry contest to capture the European light heavyweight belt.
The arena became quiet for a extremely emotional memorial ahead of the contest as 10 bells tolled in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime faded, the stillness gave way to a shout of "there's only one Ricky Hatton".
The action inside the ropes matched the emotion. Arthur was floored by a left hook directly to the face in the early round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up soon, heavy swelling forming under his face as the fighters traded punishing blows.
Rea, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the verdict with judges scorecards of 114-114, close margin and wider gap, but the two athletes were relentless and full of heart, exactly what their inspiration the legend embodied.
