UK light heavyweight Buatsi secured a victory yet unimpressive start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a competitive 10-round contest at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a contest where the approaches failed to mesh, with constant grabbing marring the contest.
Two judges had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi commented in the ringside as he was met by disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, merited the decision but the contender endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Affair
Buatsi's progress has plateaued in recent times through management issues and long spells of lack of fights.
Previously predicted as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers willing to take risks in a calculated initial 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 halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a protective stance to edge the more effective rounds.
The crowd's patience wore thin during regular grabbing, with the challenger going down various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Memorial Inspires All-Manchester Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester contest to secure the European light-heavyweight championship.
The arena became quiet for a extremely emotional tribute prior to the bout as 10 bells rang in honor of the city's native Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the city since Hatton's passing. As the final chime disappeared, the quiet became a chant of "there's just one Ricky Hatton".
The action within the ring reflected the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the second round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was damaged early, noticeable damage appearing under his face as the duo traded punishing blows.
The challenger, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur edged the decision with judges scorecards of even score, close margin and 115-112, but the two athletes were relentless and full of heart, exactly what their hero the legend stood for.
