UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the ring as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a twentieth professional win.
Some ringside observers believed Parker, thirty-one, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-fight professional journey.
Buatsi Secures Triumph in Slow Encounter
His career development has stalled in recent years through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He began cautiously, with both competitors willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to narrowly win the more effective rounds.
The audience's tolerance decreased because of constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker finished the stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Inspires Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester contest to secure the European light heavyweight title.
The venue grew hushed for a deeply poignant homage ahead of the contest as 10 bells sounded in remembrance of local hero Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the last bell faded, the stillness transitioned to a chant of "there's only one Hatton".
The fighting inside the ropes equaled the feeling. The eventual winner was floored by a significant blow flush on the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was marked up quickly, significant bruising forming under his eye as the pair exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over 12 rounds.
Arthur narrowly won the result with scoring tallies of 114-114, close margin and 115-112, but both fighters were persistent and brave, everything their idol the legend represented.
